NMAP = Net Mapper 公式Doc 日本語 doc URL https://nmap.org/man/ja/ この日本語版は4.50について記述してあると2025-10-06時点で記載がある。最新版は7系と、ドキュメントがだいぶ古いので、だれか翻訳してあげたら喜ばれると思う。(他の言語の翻訳も全てバージョンだけ確認したが、イタリアについて日本が2番目に新しかった。あまり翻訳活動は活発でないのかもしれない。) 英語 doc https://nmap.org/book/toc.html Example セクションがたくさんある。 movies movies セクションがあっておもろい https://nmap.org/movies/ download https://nmap.org/download 手元のnmap version $ nmap --version Nmap version 7.94SVN ( https://nmap.org ) Platform: x86_64-pc-linux-gnu Compiled with: liblua-5.4.6 openssl-3.0.13 libssh2-1.11.0 libz-1.3 libpcre2-10.42 libpcap-1.10.4 nmap-libdnet-1.12 ipv6 Compiled without: Available nsock engines: epoll poll select man より引用 NMAP(1) Nmap Reference Guide NMAP(1) NAME nmap - Network exploration tool and security / port scanner SYNOPSIS nmap [Scan Type...] [Options] {target specification} DESCRIPTION Nmap (“Network Mapper”) is an open source tool for network exploration and security auditing. It was designed to rapidly scan large networks, although it works fine against single hosts. Nmap uses raw IP packets in novel ways to determine what hosts are available on the network, what services (application name and version) those hosts are offering, what operating systems (and OS versions) they are running, what type of packet filters/firewalls are in use, and dozens of other characteristics. While Nmap is commonly used for security audits, many systems and network administrators find it useful for routine tasks such as network inventory, managing service upgrade schedules, and monitoring host or service uptime. The output from Nmap is a list of scanned targets, with supplemental information on each depending on the options used. Key among that information is the “interesting ports table”. That table lists the port number and protocol, service name, and state. The state is either open, filtered, closed, or unfiltered. Open means that an application on the target machine is listening for connections/packets on that port. Filtered means that a firewall, filter, or other network obstacle is blocking the port so that Nmap cannot tell whether it is open or closed. Closed ports have no application listening on them, though they could open up at any time. Ports are classified as unfiltered when they are responsive to Nmap's probes, but Nmap cannot determine whether they are open or closed. Nmap reports the state combinations open|filtered and closed|filtered when it cannot determine which of the two states describe a port. The port table may also include software version details when version detection has been requested. When an IP protocol scan is requested (-sO), Nmap provides information on supported IP protocols rather than listening ports. In addition to the interesting ports table, Nmap can provide further information on targets, including reverse DNS names, operating system guesses, device types, and MAC addresses. A typical Nmap scan is shown in Example 1. The only Nmap arguments used in this example are -A, to enable OS and version detection, script scanning, and traceroute; -T4 for faster execution; and then the hostname. Example 1. A representative Nmap scan # nmap -A -T4 scanme.nmap.org Nmap scan report for scanme.nmap.org (74.207.244.221) Host is up (0.029s latency). rDNS record for 74.207.244.221: li86-221.members.linode.com Not shown: 995 closed ports PORT STATE SERVICE VERSION 22/tcp open ssh OpenSSH 5.3p1 Debian 3ubuntu7 (protocol 2.0) | ssh-hostkey: 1024 8d:60:f1:7c:ca:b7:3d:0a:d6:67:54:9d:69:d9:b9:dd (DSA) |_2048 79:f8:09:ac:d4:e2:32:42:10:49:d3:bd:20:82:85:ec (RSA) 80/tcp open http Apache httpd 2.2.14 ((Ubuntu)) |_http-title: Go ahead and ScanMe! 646/tcp filtered ldp 1720/tcp filtered H.323/Q.931 9929/tcp open nping-echo Nping echo Device type: general purpose Running: Linux 2.6.X OS CPE: cpe:/o:linux:linux_kernel:2.6.39 OS details: Linux 2.6.39 Network Distance: 11 hops Service Info: OS: Linux; CPE: cpe:/o:linux:kernel TRACEROUTE (using port 53/tcp) HOP RTT ADDRESS [Cut first 10 hops for brevity] 11 17.65 ms li86-221.members.linode.com (74.207.244.221) Nmap done: 1 IP address (1 host up) scanned in 14.40 seconds The newest version of Nmap can be obtained from https://nmap.org. The newest version of this man page is available at https://nmap.org/book/man.html. It is also included as a chapter of Nmap Network Scanning: The Official Nmap Project Guide to Network Discovery and Security Scanning (see https://nmap.org/book/). OPTIONS SUMMARY This options summary is printed when Nmap is run with no arguments, and the latest version is always available at https://svn.nmap.org/nmap/docs/nmap.usage.txt. It helps people remember the most common options, but is no substitute for the in-depth documentation in the rest of this manual. Some obscure options aren't even included here. Nmap 7.94 ( https://nmap.org ) Usage: nmap [Scan Type(s)] [Options] {target specification} TARGET SPECIFICATION: Can pass hostnames, IP addresses, networks, etc. Ex: scanme.nmap.org, microsoft.com/24, 192.168.0.1; 10.0.0-255.1-254 -iL <inputfilename>: Input from list of hosts/networks -iR <num hosts>: Choose random targets --exclude <host1[,host2][,host3],...>: Exclude hosts/networks --excludefile <exclude_file>: Exclude list from file HOST DISCOVERY: -sL: List Scan - simply list targets to scan -sn: Ping Scan - disable port scan -Pn: Treat all hosts as online -- skip host discovery -PS/PA/PU/PY[portlist]: TCP SYN/ACK, UDP or SCTP discovery to given ports -PE/PP/PM: ICMP echo, timestamp, and netmask request discovery probes -PO[protocol list]: IP Protocol Ping -n/-R: Never do DNS resolution/Always resolve [default: sometimes] --dns-servers <serv1[,serv2],...>: Specify custom DNS servers --system-dns: Use OS's DNS resolver --traceroute: Trace hop path to each host SCAN TECHNIQUES: -sS/sT/sA/sW/sM: TCP SYN/Connect()/ACK/Window/Maimon scans -sU: UDP Scan -sN/sF/sX: TCP Null, FIN, and Xmas scans --scanflags <flags>: Customize TCP scan flags -sI <zombie host[:probeport]>: Idle scan -sY/sZ: SCTP INIT/COOKIE-ECHO scans -sO: IP protocol scan -b <FTP relay host>: FTP bounce scan PORT SPECIFICATION AND SCAN ORDER: -p <port ranges>: Only scan specified ports Ex: -p22; -p1-65535; -p U:53,111,137,T:21-25,80,139,8080,S:9 --exclude-ports <port ranges>: Exclude the specified ports from scanning -F: Fast mode - Scan fewer ports than the default scan -r: Scan ports sequentially - don't randomize --top-ports <number>: Scan <number> most common ports --port-ratio <ratio>: Scan ports more common than <ratio> SERVICE/VERSION DETECTION: -sV: Probe open ports to determine service/version info --version-intensity <level>: Set from 0 (light) to 9 (try all probes) --version-light: Limit to most likely probes (intensity 2) --version-all: Try every single probe (intensity 9) --version-trace: Show detailed version scan activity (for debugging) SCRIPT SCAN: -sC: equivalent to --script=default --script=<Lua scripts>: <Lua scripts> is a comma separated list of directories, script-files or script-categories --script-args=<n1=v1,[n2=v2,...]>: provide arguments to scripts --script-args-file=filename: provide NSE script args in a file --script-trace: Show all data sent and received --script-updatedb: Update the script database. --script-help=<Lua scripts>: Show help about scripts. <Lua scripts> is a comma-separated list of script-files or script-categories. OS DETECTION: -O: Enable OS detection --osscan-limit: Limit OS detection to promising targets --osscan-guess: Guess OS more aggressively TIMING AND PERFORMANCE: Options which take <time> are in seconds, or append 'ms' (milliseconds), 's' (seconds), 'm' (minutes), or 'h' (hours) to the value (e.g. 30m). -T<0-5>: Set timing template (higher is faster) --min-hostgroup/max-hostgroup <size>: Parallel host scan group sizes --min-parallelism/max-parallelism <numprobes>: Probe parallelization --min-rtt-timeout/max-rtt-timeout/initial-rtt-timeout <time>: Specifies probe round trip time. --max-retries <tries>: Caps number of port scan probe retransmissions. --host-timeout <time>: Give up on target after this long --scan-delay/--max-scan-delay <time>: Adjust delay between probes --min-rate <number>: Send packets no slower than <number> per second --max-rate <number>: Send packets no faster than <number> per second FIREWALL/IDS EVASION AND SPOOFING: -f; --mtu <val>: fragment packets (optionally w/given MTU) -D <decoy1,decoy2[,ME],...>: Cloak a scan with decoys -S <IP_Address>: Spoof source address -e <iface>: Use specified interface -g/--source-port <portnum>: Use given port number --proxies <url1,[url2],...>: Relay connections through HTTP/SOCKS4 proxies --data <hex string>: Append a custom payload to sent packets --data-string <string>: Append a custom ASCII string to sent packets --data-length <num>: Append random data to sent packets --ip-options <options>: Send packets with specified ip options --ttl <val>: Set IP time-to-live field --spoof-mac <mac address/prefix/vendor name>: Spoof your MAC address --badsum: Send packets with a bogus TCP/UDP/SCTP checksum OUTPUT: -oN/-oX/-oS/-oG <file>: Output scan in normal, XML, s|<rIpt kIddi3, and Grepable format, respectively, to the given filename. -oA <basename>: Output in the three major formats at once -v: Increase verbosity level (use -vv or more for greater effect) -d: Increase debugging level (use -dd or more for greater effect) --reason: Display the reason a port is in a particular state --open: Only show open (or possibly open) ports --packet-trace: Show all packets sent and received --iflist: Print host interfaces and routes (for debugging) --append-output: Append to rather than clobber specified output files --resume <filename>: Resume an aborted scan --noninteractive: Disable runtime interactions via keyboard --stylesheet <path/URL>: XSL stylesheet to transform XML output to HTML --webxml: Reference stylesheet from Nmap.Org for more portable XML --no-stylesheet: Prevent associating of XSL stylesheet w/XML output MISC: -6: Enable IPv6 scanning -A: Enable OS detection, version detection, script scanning, and traceroute --datadir <dirname>: Specify custom Nmap data file location --send-eth/--send-ip: Send using raw ethernet frames or IP packets --privileged: Assume that the user is fully privileged --unprivileged: Assume the user lacks raw socket privileges -V: Print version number -h: Print this help summary page. EXAMPLES: nmap -v -A scanme.nmap.org nmap -v -sn 192.168.0.0/16 10.0.0.0/8 nmap -v -iR 10000 -Pn -p 80 SEE THE MAN PAGE (https://nmap.org/book/man.html) FOR MORE OPTIONS AND EXAMPLES TARGET SPECIFICATION Everything on the Nmap command-line that isn't an option (or option argument) is treated as a target host specification. The simplest case is to specify a target IP address or hostname for scanning. When a hostname is given as a target, it is resolved via the Domain Name System (DNS) to determine the IP address to scan. If the name resolves to more than one IP address, only the first one will be scanned. To make Nmap scan all the resolved addresses instead of only the first one, use the --resolve-all option. Sometimes you wish to scan a whole network of adjacent hosts. For this, Nmap supports CIDR-style addressing. You can append /numbits to an IP address or hostname and Nmap will scan every IP address for which the first numbits are the same as for the reference IP or hostname given. For example, 192.168.10.0/24 would scan the 256 hosts between 192.168.10.0 (binary: 11000000 10101000 00001010 00000000) and 192.168.10.255 (binary: 11000000 10101000 00001010 11111111), inclusive. 192.168.10.40/24 would scan exactly the same targets. Given that the host scanme.nmap.org is at the IP address 64.13.134.52, the specification scanme.nmap.org/16 would scan the 65,536 IP addresses between 64.13.0.0 and 64.13.255.255. The smallest allowed value is /0, which targets the whole Internet. The largest value for IPv4 is /32, which scans just the named host or IP address because all address bits are fixed. The largest value for IPv6 is /128, which does the same thing. CIDR notation is short but not always flexible enough. For example, you might want to scan 192.168.0.0/16 but skip any IPs ending with .0 or .255 because they may be used as subnet network and broadcast addresses. Nmap supports this through octet range addressing. Rather than specify a normal IP address, you can specify a comma-separated list of numbers or ranges for each octet. For example, 192.168.0-255.1-254 will skip all addresses in the range that end in .0 or .255, and 192.168.3-5,7.1 will scan the four addresses 192.168.3.1, 192.168.4.1, 192.168.5.1, and 192.168.7.1. Either side of a range may be omitted; the default values are 0 on the left and 255 on the right. Using - by itself is the same as 0-255, but remember to use 0- in the first octet so the target specification doesn't look like a command-line option. Ranges need not be limited to the final octets: the specifier 0-255.0-255.13.37 will perform an Internet-wide scan for all IP addresses ending in 13.37. This sort of broad sampling can be useful for Internet surveys and research. IPv6 addresses can be specified by their fully qualified IPv6 address or hostname or with CIDR notation for subnets. Octet ranges aren't yet supported for IPv6. IPv6 addresses with non-global scope need to have a zone ID suffix. On Unix systems, this is a percent sign followed by an interface name; a complete address might be fe80::a8bb:ccff:fedd:eeff%eth0. On Windows, use an interface index number in place of an interface name: fe80::a8bb:ccff:fedd:eeff%1. You can see a list of interface indexes by running the command netsh.exe interface ipv6 show interface. Nmap accepts multiple host specifications on the command line, and they don't need to be the same type. The command nmap scanme.nmap.org 192.168.0.0/8 10.0.0,1,3-7.- does what you would expect. While targets are usually specified on the command lines, the following options are also available to control target selection: -iL inputfilename (Input from list) Reads target specifications from inputfilename. Passing a huge list of hosts is often awkward on the command line, yet it is a common desire. For example, your DHCP server might export a list of 10,000 current leases that you wish to scan. Or maybe you want to scan all IP addresses except for those to locate hosts using unauthorized static IP addresses. Simply generate the list of hosts to scan and pass that filename to Nmap as an argument to the -iL option. Entries can be in any of the formats accepted by Nmap on the command line (IP address, hostname, CIDR, IPv6, or octet ranges). Each entry must be separated by one or more spaces, tabs, or newlines. You can specify a hyphen (-) as the filename if you want Nmap to read hosts from standard input rather than an actual file. The input file may contain comments that start with # and extend to the end of the line. -iR num hosts (Choose random targets) For Internet-wide surveys and other research, you may want to choose targets at random. The num hosts argument tells Nmap how many IPs to generate. Undesirable IPs such as those in certain private, multicast, or unallocated address ranges are automatically skipped. The argument 0 can be specified for a never-ending scan. Keep in mind that some network administrators bristle at unauthorized scans of their networks and may complain. Use this option at your own risk! If you find yourself really bored one rainy afternoon, try the command nmap -Pn -sS -p 80 -iR 0 --open to locate random web servers for browsing. --exclude host1[,host2[,...]] (Exclude hosts/networks) Specifies a comma-separated list of targets to be excluded from the scan even if they are part of the overall network range you specify. The list you pass in uses normal Nmap syntax, so it can include hostnames, CIDR netblocks, octet ranges, etc. This can be useful when the network you wish to scan includes untouchable mission-critical servers, systems that are known to react adversely to port scans, or subnets administered by other people. --excludefile exclude_file (Exclude list from file) This offers the same functionality as the --exclude option, except that the excluded targets are provided in a newline-, space-, or tab-delimited exclude_file rather than on the command line. The exclude file may contain comments that start with # and extend to the end of the line. -n (No DNS resolution) Tells Nmap to never do reverse DNS resolution on the active IP addresses it finds. Since DNS can be slow even with Nmap's built-in parallel stub resolver, this option can slash scanning times. -R (DNS resolution for all targets) Tells Nmap to always do reverse DNS resolution on the target IP addresses. Normally reverse DNS is only performed against responsive (online) hosts. --resolve-all (Scan each resolved address) If a hostname target resolves to more than one address, scan all of them. The default behavior is to only scan the first resolved address. Regardless, only addresses in the appropriate address family will be scanned: IPv4 by default, IPv6 with -6. --unique (Scan each address only once) Scan each IP address only once. The default behavior is to scan each address as many times as it is specified in the target list, such as when network ranges overlap or different hostnames resolve to the same address. --system-dns (Use system DNS resolver) By default, Nmap reverse-resolves IP addresses by sending queries directly to the name servers configured on your host and then listening for responses. Many requests (often dozens) are performed in parallel to improve performance. Specify this option to use your system resolver instead (one IP at a time via the getnameinfo call). This is slower and rarely useful unless you find a bug in the Nmap parallel resolver (please let us know if you do). The system resolver is always used for forward lookups (getting an IP address from a hostname). --dns-servers server1[,server2[,...]] (Servers to use for reverse DNS queries) By default, Nmap determines your DNS servers (for rDNS resolution) from your resolv.conf file (Unix) or the Registry (Win32). Alternatively, you may use this option to specify alternate servers. This option is not honored if you are using --system-dns. Using multiple DNS servers is often faster, especially if you choose authoritative servers for your target IP space. This option can also improve stealth, as your requests can be bounced off just about any recursive DNS server on the Internet. This option also comes in handy when scanning private networks. Sometimes only a few name servers provide proper rDNS information, and you may not even know where they are. You can scan the network for port 53 (perhaps with version detection), then try Nmap list scans (-sL) specifying each name server one at a time with --dns-servers until you find one which works. This option might not be honored if the DNS response exceeds the size of a UDP packet. In such a situation our DNS resolver will make the best effort to extract a response from the truncated packet, and if not successful it will fall back to using the system resolver. Also, responses that contain CNAME aliases will fall back to the system resolver. HOST DISCOVERY One of the very first steps in any network reconnaissance mission is to reduce a (sometimes huge) set of IP ranges into a list of active or interesting hosts. Scanning every port of every single IP address is slow and usually unnecessary. Of course what makes a host interesting depends greatly on the scan purposes. Network administrators may only be interested in hosts running a certain service, while security auditors may care about every single device with an IP address. An administrator may be comfortable using just an ICMP ping to locate hosts on his internal network, while an external penetration tester may use a diverse set of dozens of probes in an attempt to evade firewall restrictions. Because host discovery needs are so diverse, Nmap offers a wide variety of options for customizing the techniques used. Host discovery is sometimes called ping scan, but it goes well beyond the simple ICMP echo request packets associated with the ubiquitous ping tool. Users can skip the discovery step entirely with a list scan (-sL) or by disabling host discovery (-Pn), or engage the network with arbitrary combinations of multi-port TCP SYN/ACK, UDP, SCTP INIT and ICMP probes. The goal of these probes is to solicit responses which demonstrate that an IP address is actually active (is being used by a host or network device). On many networks, only a small percentage of IP addresses are active at any given time. This is particularly common with private address space such as 10.0.0.0/8. That network has 16 million IPs, but I have seen it used by companies with less than a thousand machines. Host discovery can find those machines in a sparsely allocated sea of IP addresses. If no host discovery options are given, Nmap sends an ICMP echo request, a TCP SYN packet to port 443, a TCP ACK packet to port 80, and an ICMP timestamp request. (For IPv6, the ICMP timestamp request is omitted because it is not part of ICMPv6.) These defaults are equivalent to the -PE -PS443 -PA80 -PP options. The exceptions to this are the ARP (for IPv4) and Neighbor Discovery (for IPv6) scans which are used for any targets on a local ethernet network. For unprivileged Unix shell users, the default probes are a SYN packet to ports 80 and 443 using the connect system call. This host discovery is often sufficient when scanning local networks, but a more comprehensive set of discovery probes is recommended for security auditing. The -P* options (which select ping types) can be combined. You can increase your odds of penetrating strict firewalls by sending many probe types using different TCP ports/flags and ICMP codes. Also note that ARP/Neighbor Discovery is done by default against targets on a local Ethernet network even if you specify other -P* options, because it is almost always faster and more effective. By default, Nmap does host discovery and then performs a port scan against each host it determines is online. This is true even if you specify non-default host discovery types such as UDP probes (-PU). Read about the -sn option to learn how to perform only host discovery, or use -Pn to skip host discovery and port scan all target addresses. The following options control host discovery: -sL (List Scan) The list scan is a degenerate form of host discovery that simply lists each host of the network(s) specified, without sending any packets to the target hosts. By default, Nmap still does reverse-DNS resolution on the hosts to learn their names. It is often surprising how much useful information simple hostnames give out. For example, fw.chi is the name of one company's Chicago firewall. Nmap also reports the total number of IP addresses at the end. The list scan is a good sanity check to ensure that you have proper IP addresses for your targets. If the hosts sport domain names you do not recognize, it is worth investigating further to prevent scanning the wrong company's network. Since the idea is to simply print a list of target hosts, options for higher level functionality such as port scanning, OS detection, or host discovery cannot be combined with this. If you wish to disable host discovery while still performing such higher level functionality, read up on the -Pn (skip host discovery) option. -sn (No port scan) This option tells Nmap not to do a port scan after host discovery, and only print out the available hosts that responded to the host discovery probes. This is often known as a “ping scan”, but you can also request that traceroute and NSE host scripts be run. This is by default one step more intrusive than the list scan, and can often be used for the same purposes. It allows light reconnaissance of a target network without attracting much attention. Knowing how many hosts are up is more valuable to attackers than the list provided by list scan of every single IP and host name. Systems administrators often find this option valuable as well. It can easily be used to count available machines on a network or monitor server availability. This is often called a ping sweep, and is more reliable than pinging the broadcast address because many hosts do not reply to broadcast queries. The default host discovery done with -sn consists of an ICMP echo request, TCP SYN to port 443, TCP ACK to port 80, and an ICMP timestamp request by default. When executed by an unprivileged user, only SYN packets are sent (using a connect call) to ports 80 and 443 on the target. When a privileged user tries to scan targets on a local ethernet network, ARP requests are used unless --send-ip was specified. The -sn option can be combined with any of the discovery probe types (the -P* options) for greater flexibility. If any of those probe type and port number options are used, the default probes are overridden. When strict firewalls are in place between the source host running Nmap and the target network, using those advanced techniques is recommended. Otherwise hosts could be missed when the firewall drops probes or their responses. In previous releases of Nmap, -sn was known as -sP. -Pn (No ping) This option skips the host discovery stage altogether. Normally, Nmap uses this stage to determine active machines for heavier scanning and to gauge the speed of the network. By default, Nmap only performs heavy probing such as port scans, version detection, or OS detection against hosts that are found to be up. Disabling host discovery with -Pn causes Nmap to attempt the requested scanning functions against every target IP address specified. So if a /16 sized network is specified on the command line, all 65,536 IP addresses are scanned. Proper host discovery is skipped as with the list scan, but instead of stopping and printing the target list, Nmap continues to perform requested functions as if each target IP is active. Default timing parameters are used, which may result in slower scans. To skip host discovery and port scan, while still allowing NSE to run, use the two options -Pn -sn together. For machines on a local ethernet network, ARP scanning will still be performed (unless --disable-arp-ping or --send-ip is specified) because Nmap needs MAC addresses to further scan target hosts. In previous versions of Nmap, -Pn was -P0 and -PN. -PS port list (TCP SYN Ping) This option sends an empty TCP packet with the SYN flag set. The default destination port is 80 (configurable at compile time by changing DEFAULT_TCP_PROBE_PORT_SPEC in nmap.h). Alternate ports can be specified as a parameter. The syntax is the same as for the -p except that port type specifiers like T: are not allowed. Examples are -PS22 and -PS22-25,80,113,1050,35000. Note that there can be no space between -PS and the port list. If multiple probes are specified they will be sent in parallel. The SYN flag suggests to the remote system that you are attempting to establish a connection. Normally the destination port will be closed, and a RST (reset) packet sent back. If the port happens to be open, the target will take the second step of a TCP three-way-handshake by responding with a SYN/ACK TCP packet. The machine running Nmap then tears down the nascent connection by responding with a RST rather than sending an ACK packet which would complete the three-way-handshake and establish a full connection. The RST packet is sent by the kernel of the machine running Nmap in response to the unexpected SYN/ACK, not by Nmap itself. Nmap does not care whether the port is open or closed. Either the RST or SYN/ACK response discussed previously tell Nmap that the host is available and responsive. On Unix boxes, only the privileged user root is generally able to send and receive raw TCP packets. For unprivileged users, a workaround is automatically employed whereby the connect system call is initiated against each target port. This has the effect of sending a SYN packet to the target host, in an attempt to establish a connection. If connect returns with a quick success or an ECONNREFUSED failure, the underlying TCP stack must have received a SYN/ACK or RST and the host is marked available. If the connection attempt is left hanging until a timeout is reached, the host is marked as down. -PA port list (TCP ACK Ping) The TCP ACK ping is quite similar to the just-discussed SYN ping. The difference, as you could likely guess, is that the TCP ACK flag is set instead of the SYN flag. Such an ACK packet purports to be acknowledging data over an established TCP connection, but no such connection exists. So remote hosts should always respond with a RST packet, disclosing their existence in the process. The -PA option uses the same default port as the SYN probe (80) and can also take a list of destination ports in the same format. If an unprivileged user tries this, the connect workaround discussed previously is used. This workaround is imperfect because connect is actually sending a SYN packet rather than an ACK. The reason for offering both SYN and ACK ping probes is to maximize the chances of bypassing firewalls. Many administrators configure routers and other simple firewalls to block incoming SYN packets except for those destined for public services like the company web site or mail server. This prevents other incoming connections to the organization, while allowing users to make unobstructed outgoing connections to the Internet. This non-stateful approach takes up few resources on the firewall/router and is widely supported by hardware and software filters. The Linux Netfilter/iptables firewall software offers the --syn convenience option to implement this stateless approach. When stateless firewall rules such as this are in place, SYN ping probes (-PS) are likely to be blocked when sent to closed target ports. In such cases, the ACK probe shines as it cuts right through these rules. Another common type of firewall uses stateful rules that drop unexpected packets. This feature was initially found mostly on high-end firewalls, though it has become much more common over the years. The Linux Netfilter/iptables system supports this through the --state option, which categorizes packets based on connection state. A SYN probe is more likely to work against such a system, as unexpected ACK packets are generally recognized as bogus and dropped. A solution to this quandary is to send both SYN and ACK probes by specifying -PS and -PA. -PU port list (UDP Ping) Another host discovery option is the UDP ping, which sends a UDP packet to the given ports. For most ports, the packet will be empty, though some use a protocol-specific payload that is more likely to elicit a response. The payloads are the same probes used in service and version detection and are defined in the nmap-service-probes file. Packet content can also be affected with the --data, --data-string, and --data-length options. The port list takes the same format as with the previously discussed -PS and -PA options. If no ports are specified, the default is 40125. This default can be configured at compile-time by changing DEFAULT_UDP_PROBE_PORT_SPEC in nmap.h. A highly uncommon port is used by default because sending to open ports is often undesirable for this particular scan type. Upon hitting a closed port on the target machine, the UDP probe should elicit an ICMP port unreachable packet in return. This signifies to Nmap that the machine is up and available. Many other types of ICMP errors, such as host/network unreachables or TTL exceeded are indicative of a down or unreachable host. A lack of response is also interpreted this way. If an open port is reached, most services simply ignore the empty packet and fail to return any response. This is why the default probe port is 40125, which is highly unlikely to be in use. A few services, such as the Character Generator (chargen) protocol, will respond to an empty UDP packet, and thus disclose to Nmap that the machine is available. The primary advantage of this scan type is that it bypasses firewalls and filters that only screen TCP. For example, I once owned a Linksys BEFW11S4 wireless broadband router. The external interface of this device filtered all TCP ports by default, but UDP probes would still elicit port unreachable messages and thus give away the device. -PY port list (SCTP INIT Ping) This option sends an SCTP packet containing a minimal INIT chunk. The default destination port is 80 (configurable at compile time by changing DEFAULT_SCTP_PROBE_PORT_SPEC in nmap.h). Alternate ports can be specified as a parameter. The syntax is the same as for the -p except that port type specifiers like S: are not allowed. Examples are -PY22 and -PY22,80,179,5060. Note that there can be no space between -PY and the port list. If multiple probes are specified they will be sent in parallel. The INIT chunk suggests to the remote system that you are attempting to establish an association. Normally the destination port will be closed, and an ABORT chunk will be sent back. If the port happens to be open, the target will take the second step of an SCTP four-way-handshake by responding with an INIT-ACK chunk. If the machine running Nmap has a functional SCTP stack, then it tears down the nascent association by responding with an ABORT chunk rather than sending a COOKIE-ECHO chunk which would be the next step in the four-way-handshake. The ABORT packet is sent by the kernel of the machine running Nmap in response to the unexpected INIT-ACK, not by Nmap itself. Nmap does not care whether the port is open or closed. Either the ABORT or INIT-ACK response discussed previously tell Nmap that the host is available and responsive. On Unix boxes, only the privileged user root is generally able to send and receive raw SCTP packets. Using SCTP INIT Pings is currently not possible for unprivileged users. -PE; -PP; -PM (ICMP Ping Types) In addition to the unusual TCP, UDP and SCTP host discovery types discussed previously, Nmap can send the standard packets sent by the ubiquitous ping program. Nmap sends an ICMP type 8 (echo request) packet to the target IP addresses, expecting a type 0 (echo reply) in return from available hosts. Unfortunately for network explorers, many hosts and firewalls now block these packets, rather than responding as required by RFC 1122[2]. For this reason, ICMP-only scans are rarely reliable enough against unknown targets over the Internet. But for system administrators monitoring an internal network, they can be a practical and efficient approach. Use the -PE option to enable this echo request behavior. While echo request is the standard ICMP ping query, Nmap does not stop there. The ICMP standards (RFC 792[3] and RFC 950[4] ) also specify timestamp request, information request, and address mask request packets as codes 13, 15, and 17, respectively. While the ostensible purpose for these queries is to learn information such as address masks and current times, they can easily be used for host discovery. A system that replies is up and available. Nmap does not currently implement information request packets, as they are not widely supported. RFC 1122 insists that “a host SHOULD NOT implement these messages”. Timestamp and address mask queries can be sent with the -PP and -PM options, respectively. A timestamp reply (ICMP code 14) or address mask reply (code 18) discloses that the host is available. These two queries can be valuable when administrators specifically block echo request packets while forgetting that other ICMP queries can be used for the same purpose. -PO protocol list (IP Protocol Ping) One of the newer host discovery options is the IP protocol ping, which sends IP packets with the specified protocol number set in their IP header. The protocol list takes the same format as do port lists in the previously discussed TCP, UDP and SCTP host discovery options. If no protocols are specified, the default is to send multiple IP packets for ICMP (protocol 1), IGMP (protocol 2), and IP-in-IP (protocol 4). The default protocols can be configured at compile-time by changing DEFAULT_PROTO_PROBE_PORT_SPEC in nmap.h. Note that for the ICMP, IGMP, TCP (protocol 6), UDP (protocol 17) and SCTP (protocol 132), the packets are sent with the proper protocol headers while other protocols are sent with no additional data beyond the IP header (unless any of --data, --data-string, or --data-length options are specified). This host discovery method looks for either responses using the same protocol as a probe, or ICMP protocol unreachable messages which signify that the given protocol isn't supported on the destination host. Either type of response signifies that the target host is alive. --disable-arp-ping (No ARP or ND Ping) Nmap normally does ARP or IPv6 Neighbor Discovery (ND) discovery of locally connected ethernet hosts, even if other host discovery options such as -Pn or -PE are used. To disable this implicit behavior, use the --disable-arp-ping option. The default behavior is normally faster, but this option is useful on networks using proxy ARP, in which a router speculatively replies to all ARP requests, making every target appear to be up according to ARP scan. --discovery-ignore-rst In some cases, firewalls may spoof TCP reset (RST) replies in response to probes to unoccupied or disallowed addresses. Since Nmap ordinarily considers RST replies to be proof that the target is up, this can lead to wasted time scanning targets that aren't there. Using the --discovery-ignore-rst will prevent Nmap from considering these replies during host discovery. You may need to select extra host discovery options to ensure you don't miss targets in this case. --traceroute (Trace path to host) Traceroutes are performed post-scan using information from the scan results to determine the port and protocol most likely to reach the target. It works with all scan types except connect scans (-sT) and idle scans (-sI). All traces use Nmap's dynamic timing model and are performed in parallel. Traceroute works by sending packets with a low TTL (time-to-live) in an attempt to elicit ICMP Time Exceeded messages from intermediate hops between the scanner and the target host. Standard traceroute implementations start with a TTL of 1 and increment the TTL until the destination host is reached. Nmap's traceroute starts with a high TTL and then decrements the TTL until it reaches zero. Doing it backwards lets Nmap employ clever caching algorithms to speed up traces over multiple hosts. On average Nmap sends 5–10 fewer packets per host, depending on network conditions. If a single subnet is being scanned (i.e. 192.168.0.0/24) Nmap may only have to send two packets to most hosts. PORT SCANNING BASICS While Nmap has grown in functionality over the years, it began as an efficient port scanner, and that remains its core function. The simple command nmap target scans 1,000 TCP ports on the host target. While many port scanners have traditionally lumped all ports into the open or closed states, Nmap is much more granular. It divides ports into six states: open, closed, filtered, unfiltered, open|filtered, or closed|filtered. These states are not intrinsic properties of the port itself, but describe how Nmap sees them. For example, an Nmap scan from the same network as the target may show port 135/tcp as open, while a scan at the same time with the same options from across the Internet might show that port as filtered. The six port states recognized by Nmap open An application is actively accepting TCP connections, UDP datagrams or SCTP associations on this port. Finding these is often the primary goal of port scanning. Security-minded people know that each open port is an avenue for attack. Attackers and pen-testers want to exploit the open ports, while administrators try to close or protect them with firewalls without thwarting legitimate users. Open ports are also interesting for non-security scans because they show services available for use on the network. closed A closed port is accessible (it receives and responds to Nmap probe packets), but there is no application listening on it. They can be helpful in showing that a host is up on an IP address (host discovery, or ping scanning), and as part of OS detection. Because closed ports are reachable, it may be worth scanning later in case some open up. Administrators may want to consider blocking such ports with a firewall. Then they would appear in the filtered state, discussed next. filtered Nmap cannot determine whether the port is open because packet filtering prevents its probes from reaching the port. The filtering could be from a dedicated firewall device, router rules, or host-based firewall software. These ports frustrate attackers because they provide so little information. Sometimes they respond with ICMP error messages such as type 3 code 13 (destination unreachable: communication administratively prohibited), but filters that simply drop probes without responding are far more common. This forces Nmap to retry several times just in case the probe was dropped due to network congestion rather than filtering. This slows down the scan dramatically. unfiltered The unfiltered state means that a port is accessible, but Nmap is unable to determine whether it is open or closed. Only the ACK scan, which is used to map firewall rulesets, classifies ports into this state. Scanning unfiltered ports with other scan types such as Window scan, SYN scan, or FIN scan, may help resolve whether the port is open. open|filtered Nmap places ports in this state when it is unable to determine whether a port is open or filtered. This occurs for scan types in which open ports give no response. The lack of response could also mean that a packet filter dropped the probe or any response it elicited. So Nmap does not know for sure whether the port is open or being filtered. The UDP, IP protocol, FIN, NULL, and Xmas scans classify ports this way. closed|filtered This state is used when Nmap is unable to determine whether a port is closed or filtered. It is only used for the IP ID idle scan. PORT SCANNING TECHNIQUES As a novice performing automotive repair, I can struggle for hours trying to fit my rudimentary tools (hammer, duct tape, wrench, etc.) to the task at hand. When I fail miserably and tow my jalopy to a real mechanic, he invariably fishes around in a huge tool chest until pulling out the perfect gizmo which makes the job seem effortless. The art of port scanning is similar. Experts understand the dozens of scan techniques and choose the appropriate one (or combination) for a given task. Inexperienced users and script kiddies, on the other hand, try to solve every problem with the default SYN scan. Since Nmap is free, the only barrier to port scanning mastery is knowledge. That certainly beats the automotive world, where it may take great skill to determine that you need a strut spring compressor, then you still have to pay thousands of dollars for it. Most of the scan types are only available to privileged users. This is because they send and receive raw packets, which requires root access on Unix systems. Using an administrator account on Windows is recommended, though Nmap sometimes works for unprivileged users on that platform when Npcap has already been loaded into the OS. Requiring root privileges was a serious limitation when Nmap was released in 1997, as many users only had access to shared shell accounts. Now, the world is different. Computers are cheaper, far more people have always-on direct Internet access, and desktop Unix systems (including Linux and Mac OS X) are prevalent. A Windows version of Nmap is now available, allowing it to run on even more desktops. For all these reasons, users have less need to run Nmap from limited shared shell accounts. This is fortunate, as the privileged options make Nmap far more powerful and flexible. While Nmap attempts to produce accurate results, keep in mind that all of its insights are based on packets returned by the target machines (or firewalls in front of them). Such hosts may be untrustworthy and send responses intended to confuse or mislead Nmap. Much more common are non-RFC-compliant hosts that do not respond as they should to Nmap probes. FIN, NULL, and Xmas scans are particularly susceptible to this problem. Such issues are specific to certain scan types and so are discussed in the individual scan type entries. This section documents the dozen or so port scan techniques supported by Nmap. Only one method may be used at a time, except that UDP scan (-sU) and any one of the SCTP scan types (-sY, -sZ) may be combined with any one of the TCP scan types. As a memory aid, port scan type options are of the form -sC, where C is a prominent character in the scan name, usually the first. The one exception to this is the deprecated FTP bounce scan (-b). By default, Nmap performs a SYN Scan, though it substitutes a connect scan if the user does not have proper privileges to send raw packets (requires root access on Unix). Of the scans listed in this section, unprivileged users can only execute connect and FTP bounce scans. -sS (TCP SYN scan) SYN scan is the default and most popular scan option for good reasons. It can be performed quickly, scanning thousands of ports per second on a fast network not hampered by restrictive firewalls. It is also relatively unobtrusive and stealthy since it never completes TCP connections. SYN scan works against any compliant TCP stack rather than depending on idiosyncrasies of specific platforms as Nmap's FIN/NULL/Xmas, Maimon and idle scans do. It also allows clear, reliable differentiation between the open, closed, and filtered states. This technique is often referred to as half-open scanning, because you don't open a full TCP connection. You send a SYN packet, as if you are going to open a real connection and then wait for a response. A SYN/ACK indicates the port is listening (open), while a RST (reset) is indicative of a non-listener. If no response is received after several retransmissions, the port is marked as filtered. The port is also marked filtered if an ICMP unreachable error (type 3, code 0, 1, 2, 3, 9, 10, or 13) is received. The port is also considered open if a SYN packet (without the ACK flag) is received in response. This can be due to an extremely rare TCP feature known as a simultaneous open or split handshake connection (see https://nmap.org/misc/split-handshake.pdf). -sT (TCP connect scan) TCP connect scan is the default TCP scan type when SYN scan is not an option. This is the case when a user does not have raw packet privileges. Instead of writing raw packets as most other scan types do, Nmap asks the underlying operating system to establish a connection with the target machine and port by issuing the connect system call. This is the same high-level system call that web browsers, P2P clients, and most other network-enabled applications use to establish a connection. It is part of a programming interface known as the Berkeley Sockets API. Rather than read raw packet responses off the wire, Nmap uses this API to obtain status information on each connection attempt. When SYN scan is available, it is usually a better choice. Nmap has less control over the high level connect call than with raw packets, making it less efficient. The system call completes connections to open target ports rather than performing the half-open reset that SYN scan does. Not only does this take longer and require more packets to obtain the same information, but target machines are more likely to log the connection. A decent IDS will catch either, but most machines have no such alarm system. Many services on your average Unix system will add a note to syslog, and sometimes a cryptic error message, when Nmap connects and then closes the connection without sending data. Truly pathetic services crash when this happens, though that is uncommon. An administrator who sees a bunch of connection attempts in her logs from a single system should know that she has been connect scanned. -sU (UDP scans) While most popular services on the Internet run over the TCP protocol, UDP[5] services are widely deployed. DNS, SNMP, and DHCP (registered ports 53, 161/162, and 67/68) are three of the most common. Because UDP scanning is generally slower and more difficult than TCP, some security auditors ignore these ports. This is a mistake, as exploitable UDP services are quite common and attackers certainly don't ignore the whole protocol. Fortunately, Nmap can help inventory UDP ports. UDP scan is activated with the -sU option. It can be combined with a TCP scan type such as SYN scan (-sS) to check both protocols during the same run. UDP scan works by sending a UDP packet to every targeted port. For some common ports such as 53 and 161, a protocol-specific payload is sent to increase response rate, but for most ports the packet is empty unless the --data, --data-string, or --data-length options are specified. If an ICMP port unreachable error (type 3, code 3) is returned, the port is closed. Other ICMP unreachable errors (type 3, codes 0, 1, 2, 9, 10, or 13) mark the port as filtered. Occasionally, a service will respond with a UDP packet, proving that it is open. If no response is received after retransmissions, the port is classified as open|filtered. This means that the port could be open, or perhaps packet filters are blocking the communication. Version detection (-sV) can be used to help differentiate the truly open ports from the filtered ones. A big challenge with UDP scanning is doing it quickly. Open and filtered ports rarely send any response, leaving Nmap to time out and then conduct retransmissions just in case the probe or response were lost. Closed ports are often an even bigger problem. They usually send back an ICMP port unreachable error. But unlike the RST packets sent by closed TCP ports in response to a SYN or connect scan, many hosts rate limit ICMP port unreachable messages by default. Linux and Solaris are particularly strict about this. For example, the Linux 2.4.20 kernel limits destination unreachable messages to one per second (in net/ipv4/icmp.c). Nmap detects rate limiting and slows down accordingly to avoid flooding the network with useless packets that the target machine will drop. Unfortunately, a Linux-style limit of one packet per second makes a 65,536-port scan take more than 18 hours. Ideas for speeding your UDP scans up include scanning more hosts in parallel, doing a quick scan of just the popular ports first, scanning from behind the firewall, and using --host-timeout to skip slow hosts. -sY (SCTP INIT scan) SCTP[6] is a relatively new alternative to the TCP and UDP protocols, combining most characteristics of TCP and UDP, and also adding new features like multi-homing and multi-streaming. It is mostly being used for SS7/SIGTRAN related services but has the potential to be used for other applications as well. SCTP INIT scan is the SCTP equivalent of a TCP SYN scan. It can be performed quickly, scanning thousands of ports per second on a fast network not hampered by restrictive firewalls. Like SYN scan, INIT scan is relatively unobtrusive and stealthy, since it never completes SCTP associations. It also allows clear, reliable differentiation between the open, closed, and filtered states. This technique is often referred to as half-open scanning, because you don't open a full SCTP association. You send an INIT chunk, as if you are going to open a real association and then wait for a response. An INIT-ACK chunk indicates the port is listening (open), while an ABORT chunk is indicative of a non-listener. If no response is received after several retransmissions, the port is marked as filtered. The port is also marked filtered if an ICMP unreachable error (type 3, code 0, 1, 2, 3, 9, 10, or 13) is received. -sN; -sF; -sX (TCP NULL, FIN, and Xmas scans) These three scan types (even more are possible with the --scanflags option described in the next section) exploit a subtle loophole in the TCP RFC[7] to differentiate between open and closed ports. Page 65 of RFC 793 says that “if the [destination] port state is CLOSED .... an incoming segment not containing a RST causes a RST to be sent in response.” Then the next page discusses packets sent to open ports without the SYN, RST, or ACK bits set, stating that: “you are unlikely to get here, but if you do, drop the segment, and return.” When scanning systems compliant with this RFC text, any packet not containing SYN, RST, or ACK bits will result in a returned RST if the port is closed and no response at all if the port is open. As long as none of those three bits are included, any combination of the other three (FIN, PSH, and URG) are OK. Nmap exploits this with three scan types: Null scan (-sN) Does not set any bits (TCP flag header is 0) FIN scan (-sF) Sets just the TCP FIN bit. Xmas scan (-sX) Sets the FIN, PSH, and URG flags, lighting the packet up like a Christmas tree. These three scan types are exactly the same in behavior except for the TCP flags set in probe packets. If a RST packet is received, the port is considered closed, while no response means it is open|filtered. The port is marked filtered if an ICMP unreachable error (type 3, code 0, 1, 2, 3, 9, 10, or 13) is received. The key advantage to these scan types is that they can sneak through certain non-stateful firewalls and packet filtering routers. Another advantage is that these scan types are a little more stealthy than even a SYN scan. Don't count on this though—most modern IDS products can be configured to detect them. The big downside is that not all systems follow RFC 793 to the letter. A number of systems send RST responses to the probes regardless of whether the port is open or not. This causes all of the ports to be labeled closed. Major operating systems that do this are Microsoft Windows, many Cisco devices, BSDI, and IBM OS/400. This scan does work against most Unix-based systems though. Another downside of these scans is that they can't distinguish open ports from certain filtered ones, leaving you with the response open|filtered. -sA (TCP ACK scan) This scan is different than the others discussed so far in that it never determines open (or even open|filtered) ports. It is used to map out firewall rulesets, determining whether they are stateful or not and which ports are filtered. The ACK scan probe packet has only the ACK flag set (unless you use --scanflags). When scanning unfiltered systems, open and closed ports will both return a RST packet. Nmap then labels them as unfiltered, meaning that they are reachable by the ACK packet, but whether they are open or closed is undetermined. Ports that don't respond, or send certain ICMP error messages back (type 3, code 0, 1, 2, 3, 9, 10, or 13), are labeled filtered. -sW (TCP Window scan) Window scan is exactly the same as ACK scan except that it exploits an implementation detail of certain systems to differentiate open ports from closed ones, rather than always printing unfiltered when a RST is returned. It does this by examining the TCP Window field of the RST packets returned. On some systems, open ports use a positive window size (even for RST packets) while closed ones have a zero window. So instead of always listing a port as unfiltered when it receives a RST back, Window scan lists the port as open or closed if the TCP Window value in that reset is positive or zero, respectively. This scan relies on an implementation detail of a minority of systems out on the Internet, so you can't always trust it. Systems that don't support it will usually return all ports closed. Of course, it is possible that the machine really has no open ports. If most scanned ports are closed but a few common port numbers (such as 22, 25, 53) are filtered, the system is most likely susceptible. Occasionally, systems will even show the exact opposite behavior. If your scan shows 1,000 open ports and three closed or filtered ports, then those three may very well be the truly open ones. -sM (TCP Maimon scan) The Maimon scan is named after its discoverer, Uriel Maimon. He described the technique in Phrack Magazine issue #49 (November 1996). Nmap, which included this technique, was released two issues later. This technique is exactly the same as NULL, FIN, and Xmas scans, except that the probe is FIN/ACK. According to RFC 793[7] (TCP), a RST packet should be generated in response to such a probe whether the port is open or closed. However, Uriel noticed that many BSD-derived systems simply drop the packet if the port is open. --scanflags (Custom TCP scan) Truly advanced Nmap users need not limit themselves to the canned scan types offered. The --scanflags option allows you to design your own scan by specifying arbitrary TCP flags. Let your creative juices flow, while evading intrusion detection systems whose vendors simply paged through the Nmap man page adding specific rules! The --scanflags argument can be a numerical flag value such as 9 (PSH and FIN), but using symbolic names is easier. Just mash together any combination of URG, ACK, PSH, RST, SYN, and FIN. For example, --scanflags URGACKPSHRSTSYNFIN sets everything, though it's not very useful for scanning. The order these are specified in is irrelevant. In addition to specifying the desired flags, you can specify a TCP scan type (such as -sA or -sF). That base type tells Nmap how to interpret responses. For example, a SYN scan considers no-response to indicate a filtered port, while a FIN scan treats the same as open|filtered. Nmap will behave the same way it does for the base scan type, except that it will use the TCP flags you specify instead. If you don't specify a base type, SYN scan is used. -sZ (SCTP COOKIE ECHO scan) SCTP COOKIE ECHO scan is a more advanced SCTP scan. It takes advantage of the fact that SCTP implementations should silently drop packets containing COOKIE ECHO chunks on open ports, but send an ABORT if the port is closed. The advantage of this scan type is that it is not as obvious a port scan than an INIT scan. Also, there may be non-stateful firewall rulesets blocking INIT chunks, but not COOKIE ECHO chunks. Don't be fooled into thinking that this will make a port scan invisible; a good IDS will be able to detect SCTP COOKIE ECHO scans too. The downside is that SCTP COOKIE ECHO scans cannot differentiate between open and filtered ports, leaving you with the state open|filtered in both cases. -sI zombie host[:probeport] (idle scan) This advanced scan method allows for a truly blind TCP port scan of the target (meaning no packets are sent to the target from your real IP address). Instead, a unique side-channel attack exploits predictable IP fragmentation ID sequence generation on the zombie host to glean information about the open ports on the target. IDS systems will display the scan as coming from the zombie machine you specify (which must be up and meet certain criteria). This fascinating scan type is too complex to fully describe in this reference guide, so I wrote and posted an informal paper with full details at https://nmap.org/book/idlescan.html. Besides being extraordinarily stealthy (due to its blind nature), this scan type permits mapping out IP-based trust relationships between machines. The port listing shows open ports from the perspective of the zombie host. So you can try scanning a target using various zombies that you think might be trusted (via router/packet filter rules). You can add a colon followed by a port number to the zombie host if you wish to probe a particular port on the zombie for IP ID changes. Otherwise Nmap will use the port it uses by default for TCP pings (80). -sO (IP protocol scan) IP protocol scan allows you to determine which IP protocols (TCP, ICMP, IGMP, etc.) are supported by target machines. This isn't technically a port scan, since it cycles through IP protocol numbers rather than TCP or UDP port numbers. Yet it still uses the -p option to select scanned protocol numbers, reports its results within the normal port table format, and even uses the same underlying scan engine as the true port scanning methods. So it is close enough to a port scan that it belongs here. Besides being useful in its own right, protocol scan demonstrates the power of open-source software. While the fundamental idea is pretty simple, I had not thought to add it nor received any requests for such functionality. Then in the summer of 2000, Gerhard Rieger conceived the idea, wrote an excellent patch implementing it, and sent it to the announce mailing list (then called nmap-hackers). I incorporated that patch into the Nmap tree and released a new version the next day. Few pieces of commercial software have users enthusiastic enough to design and contribute their own improvements! Protocol scan works in a similar fashion to UDP scan. Instead of iterating through the port number field of a UDP packet, it sends IP packet headers and iterates through the eight-bit IP protocol field. The headers are usually empty, containing no data and not even the proper header for the claimed protocol. The exceptions are TCP, UDP, ICMP, SCTP, and IGMP. A proper protocol header for those is included since some systems won't send them otherwise and because Nmap already has functions to create them. Instead of watching for ICMP port unreachable messages, protocol scan is on the lookout for ICMP protocol unreachable messages. If Nmap receives any response in any protocol from the target host, Nmap marks that protocol as open. An ICMP protocol unreachable error (type 3, code 2) causes the protocol to be marked as closed while port unreachable (type 3, code 3) marks the protocol open. Other ICMP unreachable errors (type 3, code 0, 1, 9, 10, or 13) cause the protocol to be marked filtered (though they prove that ICMP is open at the same time). If no response is received after retransmissions, the protocol is marked open|filtered -b FTP relay host (FTP bounce scan) An interesting feature of the FTP protocol (RFC 959[8]) is support for so-called proxy FTP connections. This allows a user to connect to one FTP server, then ask that files be sent to a third-party server. Such a feature is ripe for abuse on many levels, so most servers have ceased supporting it. One of the abuses this feature allows is causing the FTP server to port scan other hosts. Simply ask the FTP server to send a file to each interesting port of a target host in turn. The error message will describe whether the port is open or not. This is a good way to bypass firewalls because organizational FTP servers are often placed where they have more access to other internal hosts than any old Internet host would. Nmap supports FTP bounce scan with the -b option. It takes an argument of the form username:password@server:port. Server is the name or IP address of a vulnerable FTP server. As with a normal URL, you may omit username:password, in which case anonymous login credentials (user: anonymous password:-wwwuser@) are used. The port number (and preceding colon) may be omitted as well, in which case the default FTP port (21) on server is used. This vulnerability was widespread in 1997 when Nmap was released, but has largely been fixed. Vulnerable servers are still around, so it is worth trying when all else fails. If bypassing a firewall is your goal, scan the target network for port 21 (or even for any FTP services if you scan all ports with version detection) and use the ftp-bounce NSE script. Nmap will tell you whether the host is vulnerable or not. If you are just trying to cover your tracks, you don't need to (and, in fact, shouldn't) limit yourself to hosts on the target network. Before you go scanning random Internet addresses for vulnerable FTP servers, consider that sysadmins may not appreciate you abusing their servers in this way. PORT SPECIFICATION AND SCAN ORDER In addition to all of the scan methods discussed previously, Nmap offers options for specifying which ports are scanned and whether the scan order is randomized or sequential. By default, Nmap scans the most common 1,000 ports for each protocol. -p port ranges (Only scan specified ports) This option specifies which ports you want to scan and overrides the default. Individual port numbers are OK, as are ranges separated by a hyphen (e.g. 1-1023). The beginning and/or end values of a range may be omitted, causing Nmap to use 1 and 65535, respectively. So you can specify -p- to scan ports from 1 through 65535. Scanning port zero is allowed if you specify it explicitly. For IP protocol scanning (-sO), this option specifies the protocol numbers you wish to scan for (0–255). When scanning a combination of protocols (e.g. TCP and UDP), you can specify a particular protocol by preceding the port numbers by T: for TCP, U: for UDP, S: for SCTP, or P: for IP Protocol. The qualifier lasts until you specify another qualifier. For example, the argument -p U:53,111,137,T:21-25,80,139,8080 would scan UDP ports 53, 111,and 137, as well as the listed TCP ports. Note that to scan both UDP and TCP, you have to specify -sU and at least one TCP scan type (such as -sS, -sF, or -sT). If no protocol qualifier is given, the port numbers are added to all protocol lists. Ports can also be specified by name according to what the port is referred to in the nmap-services. You can even use the wildcards * and ? with the names. For example, to scan FTP and all ports whose names begin with “http”, use -p ftp,http*. Be careful about shell expansions and quote the argument to -p if unsure. Ranges of ports can be surrounded by square brackets to indicate ports inside that range that appear in nmap-services. For example, the following will scan all ports in nmap-services equal to or below 1024: -p [-1024]. Be careful with shell expansions and quote the argument to -p if unsure. --exclude-ports port ranges (Exclude the specified ports from scanning) This option specifies which ports you do want Nmap to exclude from scanning. The port ranges are specified similar to -p. For IP protocol scanning (-sO), this option specifies the protocol numbers you wish to exclude (0–255). When ports are asked to be excluded, they are excluded from all types of scans (i.e. they will not be scanned under any circumstances). This also includes the discovery phase. -F (Fast (limited port) scan) Specifies that you wish to scan fewer ports than the default. Normally Nmap scans the most common 1,000 ports for each scanned protocol. With -F, this is reduced to 100. Nmap needs an nmap-services file with frequency information in order to know which ports are the most common. If port frequency information isn't available, perhaps because of the use of a custom nmap-services file, Nmap scans all named ports plus ports 1-1024. In that case, -F means to scan only ports that are named in the services file. -r (Don't randomize ports) By default, Nmap randomizes the scanned port order (except that certain commonly accessible ports are moved near the beginning for efficiency reasons). This randomization is normally desirable, but you can specify -r for sequential (sorted from lowest to highest) port scanning instead. --port-ratio ratio<decimal number between 0 and 1> Scans all ports in nmap-services file with a ratio greater than the one given. ratio must be between 0.0 and 1.0. --top-ports n Scans the n highest-ratio ports found in nmap-services file after excluding all ports specified by --exclude-ports. n must be 1 or greater. SERVICE AND VERSION DETECTION Point Nmap at a remote machine and it might tell you that ports 25/tcp, 80/tcp, and 53/udp are open. Using its nmap-services database of about 2,200 well-known services, Nmap would report that those ports probably correspond to a mail server (SMTP), web server (HTTP), and name server (DNS) respectively. This lookup is usually accurate—the vast majority of daemons listening on TCP port 25 are, in fact, mail servers. However, you should not bet your security on this! People can and do run services on strange ports. Even if Nmap is right, and the hypothetical server above is running SMTP, HTTP, and DNS servers, that is not a lot of information. When doing vulnerability assessments (or even simple network inventories) of your companies or clients, you really want to know which mail and DNS servers and versions are running. Having an accurate version number helps dramatically in determining which exploits a server is vulnerable to. Version detection helps you obtain this information. After TCP and/or UDP ports are discovered using one of the other scan methods, version detection interrogates those ports to determine more about what is actually running. The nmap-service-probes database contains probes for querying various services and match expressions to recognize and parse responses. Nmap tries to determine the service protocol (e.g. FTP, SSH, Telnet, HTTP), the application name (e.g. ISC BIND, Apache httpd, Solaris telnetd), the version number, hostname, device type (e.g. printer, router), the OS family (e.g. Windows, Linux). When possible, Nmap also gets the Common Platform Enumeration (CPE) representation of this information. Sometimes miscellaneous details like whether an X server is open to connections, the SSH protocol version, or the KaZaA user name, are available. Of course, most services don't provide all of this information. If Nmap was compiled with OpenSSL support, it will connect to SSL servers to deduce the service listening behind that encryption layer. Some UDP ports are left in the open|filtered state after a UDP port scan is unable to determine whether the port is open or filtered. Version detection will try to elicit a response from these ports (just as it does with open ports), and change the state to open if it succeeds. open|filtered TCP ports are treated the same way. Note that the Nmap -A option enables version detection among other things. A paper documenting the workings, usage, and customization of version detection is available at https://nmap.org/book/vscan.html. When RPC services are discovered, the Nmap RPC grinder is automatically used to determine the RPC program and version numbers. It takes all the TCP/UDP ports detected as RPC and floods them with SunRPC program NULL commands in an attempt to determine whether they are RPC ports, and if so, what program and version number they serve up. Thus you can effectively obtain the same info as rpcinfo -p even if the target's portmapper is behind a firewall (or protected by TCP wrappers). Decoys do not currently work with RPC scan. When Nmap receives responses from a service but cannot match them to its database, it prints out a special fingerprint and a URL for you to submit it to if you know for sure what is running on the port. Please take a couple minutes to make the submission so that your find can benefit everyone. Thanks to these submissions, Nmap has about 6,500 pattern matches for more than 650 protocols such as SMTP, FTP, HTTP, etc. Version detection is enabled and controlled with the following options: -sV (Version detection) Enables version detection, as discussed above. Alternatively, you can use -A, which enables version detection among other things. -sR is an alias for -sV. Prior to March 2011, it was used to active the RPC grinder separately from version detection, but now these options are always combined. --allports (Don't exclude any ports from version detection) By default, Nmap version detection skips TCP port 9100 because some printers simply print anything sent to that port, leading to dozens of pages of HTTP GET requests, binary SSL session requests, etc. This behavior can be changed by modifying or removing the Exclude directive in nmap-service-probes, or you can specify --allports to scan all ports regardless of any Exclude directive. --version-intensity intensity (Set version scan intensity) When performing a version scan (-sV), Nmap sends a series of probes, each of which is assigned a rarity value between one and nine. The lower-numbered probes are effective against a wide variety of common services, while the higher-numbered ones are rarely useful. The intensity level specifies which probes should be applied. The higher the number, the more likely it is the service will be correctly identified. However, high intensity scans take longer. The intensity must be between 0 and 9. The default is 7. When a probe is registered to the target port via the nmap-service-probes ports directive, that probe is tried regardless of intensity level. This ensures that the DNS probes will always be attempted against any open port 53, the SSL probe will be done against 443, etc. --version-light (Enable light mode) This is a convenience alias for --version-intensity 2. This light mode makes version scanning much faster, but it is slightly less likely to identify services. --version-all (Try every single probe) An alias for --version-intensity 9, ensuring that every single probe is attempted against each port. --version-trace (Trace version scan activity) This causes Nmap to print out extensive debugging info about what version scanning is doing. It is a subset of what you get with --packet-trace. OS DETECTION One of Nmap's best-known features is remote OS detection using TCP/IP stack fingerprinting. Nmap sends a series of TCP and UDP packets to the remote host and examines practically every bit in the responses. After performing dozens of tests such as TCP ISN sampling, TCP options support and ordering, IP ID sampling, and the initial window size check, Nmap compares the results to its nmap-os-db database of more than 2,600 known OS fingerprints and prints out the OS details if there is a match. Each fingerprint includes a freeform textual description of the OS, and a classification which provides the vendor name (e.g. Sun), underlying OS (e.g. Solaris), OS generation (e.g. 10), and device type (general purpose, router, switch, game console, etc). Most fingerprints also have a Common Platform Enumeration (CPE) representation, like cpe:/o:linux:linux_kernel:2.6. If Nmap is unable to guess the OS of a machine, and conditions are good (e.g. at least one open port and one closed port were found), Nmap will provide a URL you can use to submit the fingerprint if you know (for sure) the OS running on the machine. By doing this you contribute to the pool of operating systems known to Nmap and thus it will be more accurate for everyone. OS detection enables some other tests which make use of information that is gathered during the process anyway. One of these is TCP Sequence Predictability Classification. This measures approximately how hard it is to establish a forged TCP connection against the remote host. It is useful for exploiting source-IP based trust relationships (rlogin, firewall filters, etc) or for hiding the source of an attack. This sort of spoofing is rarely performed any more, but many machines are still vulnerable to it. The actual difficulty number is based on statistical sampling and may fluctuate. It is generally better to use the English classification such as “worthy challenge” or “trivial joke”. This is only reported in normal output in verbose (-v) mode. When verbose mode is enabled along with -O, IP ID sequence generation is also reported. Most machines are in the “incremental” class, which means that they increment the ID field in the IP header for each packet they send. This makes them vulnerable to several advanced information gathering and spoofing attacks. Another bit of extra information enabled by OS detection is a guess at a target's uptime. This uses the TCP timestamp option (RFC 1323[9]) to guess when a machine was last rebooted. The guess can be inaccurate due to the timestamp counter not being initialized to zero or the counter overflowing and wrapping around, so it is printed only in verbose mode. A paper documenting the workings, usage, and customization of OS detection is available at https://nmap.org/book/osdetect.html. OS detection is enabled and controlled with the following options: -O (Enable OS detection) Enables OS detection, as discussed above. Alternatively, you can use -A to enable OS detection along with other things. --osscan-limit (Limit OS detection to promising targets) OS detection is far more effective if at least one open and one closed TCP port are found. Set this option and Nmap will not even try OS detection against hosts that do not meet this criteria. This can save substantial time, particularly on -Pn scans against many hosts. It only matters when OS detection is requested with -O or -A. --osscan-guess; --fuzzy (Guess OS detection results) When Nmap is unable to detect a perfect OS match, it sometimes offers up near-matches as possibilities. The match has to be very close for Nmap to do this by default. Either of these (equivalent) options make Nmap guess more aggressively. Nmap will still tell you when an imperfect match is printed and display its confidence level (percentage) for each guess. --max-os-tries (Set the maximum number of OS detection tries against a target) When Nmap performs OS detection against a target and fails to find a perfect match, it usually repeats the attempt. By default, Nmap tries five times if conditions are favorable for OS fingerprint submission, and twice when conditions aren't so good. Specifying a lower --max-os-tries value (such as 1) speeds Nmap up, though you miss out on retries which could potentially identify the OS. Alternatively, a high value may be set to allow even more retries when conditions are favorable. This is rarely done, except to generate better fingerprints for submission and integration into the Nmap OS database. NMAP SCRIPTING ENGINE (NSE) The Nmap Scripting Engine (NSE) is one of Nmap's most powerful and flexible features. It allows users to write (and share) simple scripts (using the Lua programming language[10] ) to automate a wide variety of networking tasks. Those scripts are executed in parallel with the speed and efficiency you expect from Nmap. Users can rely on the growing and diverse set of scripts distributed with Nmap, or write their own to meet custom needs. Tasks we had in mind when creating the system include network discovery, more sophisticated version detection, vulnerability detection. NSE can even be used for vulnerability exploitation. To reflect those different uses and to simplify the choice of which scripts to run, each script contains a field associating it with one or more categories. Currently defined categories are auth, broadcast, default. discovery, dos, exploit, external, fuzzer, intrusive, malware, safe, version, and vuln. These are all described at https://nmap.org/book/nse-usage.html#nse-categories. Scripts are not run in a sandbox and thus could accidentally or maliciously damage your system or invade your privacy. Never run scripts from third parties unless you trust the authors or have carefully audited the scripts yourself. The Nmap Scripting Engine is described in detail at https://nmap.org/book/nse.html and is controlled by the following options: -sC Performs a script scan using the default set of scripts. It is equivalent to --script=default. Some of the scripts in this category are considered intrusive and should not be run against a target network without permission. --script filename|category|directory/|expression[,...] Runs a script scan using the comma-separated list of filenames, script categories, and directories. Each element in the list may also be a Boolean expression describing a more complex set of scripts. Each element is interpreted first as an expression, then as a category, and finally as a file or directory name. There are two special features for advanced users only. One is to prefix script names and expressions with + to force them to run even if they normally wouldn't (e.g. the relevant service wasn't detected on the target port). The other is that the argument all may be used to specify every script in Nmap's database. Be cautious with this because NSE contains dangerous scripts such as exploits, brute force authentication crackers, and denial of service attacks. File and directory names may be relative or absolute. Absolute names are used directly. Relative paths are looked for in the scripts of each of the following places until found: --datadir $NMAPDIR ~/.nmap (not searched on Windows) APPDATA\nmap (only on Windows) the directory containing the nmap executable the directory containing the nmap executable, followed by ../share/nmap (not searched on Windows) NMAPDATADIR (not searched on Windows) the current directory. When a directory name ending in / is given, Nmap loads every file in the directory whose name ends with .nse. All other files are ignored and directories are not searched recursively. When a filename is given, it does not have to have the .nse extension; it will be added automatically if necessary. Nmap scripts are stored in a scripts subdirectory of the Nmap data directory by default (see https://nmap.org/book/data-files.html). For efficiency, scripts are indexed in a database stored in scripts/script.db, which lists the category or categories in which each script belongs. When referring to scripts from script.db by name, you can use a shell-style ‘*’ wildcard. nmap --script "http-*" Loads all scripts whose name starts with http-, such as http-auth and http-open-proxy. The argument to --script had to be in quotes to protect the wildcard from the shell. More complicated script selection can be done using the and, or, and not operators to build Boolean expressions. The operators have the same precedence[11] as in Lua: not is the highest, followed by and and then or. You can alter precedence by using parentheses. Because expressions contain space characters it is necessary to quote them. nmap --script "not intrusive" Loads every script except for those in the intrusive category. nmap --script "default or safe" This is functionally equivalent to nmap --script "default,safe". It loads all scripts that are in the default category or the safe category or both. nmap --script "default and safe" Loads those scripts that are in both the default and safe categories. nmap --script "(default or safe or intrusive) and not http-*" Loads scripts in the default, safe, or intrusive categories, except for those whose names start with http-. --script-args n1=v1,n2={n3=v3},n4={v4,v5} Lets you provide arguments to NSE scripts. Arguments are a comma-separated list of name=value pairs. Names and values may be strings not containing whitespace or the characters ‘{’, ‘}’, ‘=’, or ‘,’. To include one of these characters in a string, enclose the string in single or double quotes. Within a quoted string, ‘\’ escapes a quote. A backslash is only used to escape quotation marks in this special case; in all other cases a backslash is interpreted literally. Values may also be tables enclosed in {}, just as in Lua. A table may contain simple string values or more name-value pairs, including nested tables. Many scripts qualify their arguments with the script name, as in xmpp-info.server_name. You may use that full qualified version to affect just the specified script, or you may pass the unqualified version (server_name in this case) to affect all scripts using that argument name. A script will first check for its fully qualified argument name (the name specified in its documentation) before it accepts an unqualified argument name. A complex example of script arguments is --script-args 'user=foo,pass=",{}=bar",whois={whodb=nofollow+ripe},xmpp-info.server_name=localhost'. The online NSE Documentation Portal at https://nmap.org/nsedoc/ lists the arguments that each script accepts. --script-args-file filename Lets you load arguments to NSE scripts from a file. Any arguments on the command line supersede ones in the file. The file can be an absolute path, or a path relative to Nmap's usual search path (NMAPDIR, etc.) Arguments can be comma-separated or newline-separated, but otherwise follow the same rules as for --script-args, without requiring special quoting and escaping, since they are not parsed by the shell. --script-help filename|category|directory|expression|all[,...] Shows help about scripts. For each script matching the given specification, Nmap prints the script name, its categories, and its description. The specifications are the same as those accepted by --script; so for example if you want help about the ftp-anon script, you would run nmap --script-help ftp-anon. In addition to getting help for individual scripts, you can use this as a preview of what scripts will be run for a specification, for example with nmap --script-help default. --script-trace This option does what --packet-trace does, just one ISO layer higher. If this option is specified all incoming and outgoing communication performed by a script is printed. The displayed information includes the communication protocol, the source, the target and the transmitted data. If more than 5% of all transmitted data is not printable, then the trace output is in a hex dump format. Specifying --packet-trace enables script tracing too. --script-updatedb This option updates the script database found in scripts/script.db which is used by Nmap to determine the available default scripts and categories. It is only necessary to update the database if you have added or removed NSE scripts from the default scripts directory or if you have changed the categories of any script. This option is generally used by itself: nmap --script-updatedb. TIMING AND PERFORMANCE One of my highest Nmap development priorities has always been performance. A default scan (nmap hostname) of a host on my local network takes a fifth of a second. That is barely enough time to blink, but adds up when you are scanning hundreds or thousands of hosts. Moreover, certain scan options such as UDP scanning and version detection can increase scan times substantially. So can certain firewall configurations, particularly response rate limiting. While Nmap utilizes parallelism and many advanced algorithms to accelerate these scans, the user has ultimate control over how Nmap runs. Expert users carefully craft Nmap commands to obtain only the information they care about while meeting their time constraints. Techniques for improving scan times include omitting non-critical tests, and upgrading to the latest version of Nmap (performance enhancements are made frequently). Optimizing timing parameters can also make a substantial difference. Those options are listed below. Some options accept a time parameter. This is specified in seconds by default, though you can append ‘ms’, ‘s’, ‘m’, or ‘h’ to the value to specify milliseconds, seconds, minutes, or hours. So the --host-timeout arguments 900000ms, 900, 900s, and 15m all do the same thing. --min-hostgroup numhosts; --max-hostgroup numhosts (Adjust parallel scan group sizes) Nmap has the ability to port scan or version scan multiple hosts in parallel. Nmap does this by dividing the target IP space into groups and then scanning one group at a time. In general, larger groups are more efficient. The downside is that host results can't be provided until the whole group is finished. So if Nmap started out with a group size of 50, the user would not receive any reports (except for the updates offered in verbose mode) until the first 50 hosts are completed. By default, Nmap takes a compromise approach to this conflict. It starts out with a group size as low as five so the first results come quickly and then increases the groupsize to as high as 1024. The exact default numbers depend on the options given. For efficiency reasons, Nmap uses larger group sizes for UDP or few-port TCP scans. When a maximum group size is specified with --max-hostgroup, Nmap will never exceed that size. Specify a minimum size with --min-hostgroup and Nmap will try to keep group sizes above that level. Nmap may have to use smaller groups than you specify if there are not enough target hosts left on a given interface to fulfill the specified minimum. Both may be set to keep the group size within a specific range, though this is rarely desired. These options do not have an effect during the host discovery phase of a scan. This includes plain ping scans (-sn). Host discovery always works in large groups of hosts to improve speed and accuracy. The primary use of these options is to specify a large minimum group size so that the full scan runs more quickly. A common choice is 256 to scan a network in /24 sized chunks. For a scan with many ports, exceeding that number is unlikely to help much. For scans of just a few port numbers, host group sizes of 2048 or more may be helpful. --min-parallelism numprobes; --max-parallelism numprobes (Adjust probe parallelization) These options control the total number of probes that may be outstanding for a host group. They are used for port scanning and host discovery. By default, Nmap calculates an ever-changing ideal parallelism based on network performance. If packets are being dropped, Nmap slows down and allows fewer outstanding probes. The ideal probe number slowly rises as the network proves itself worthy. These options place minimum or maximum bounds on that variable. By default, the ideal parallelism can drop to one if the network proves unreliable and rise to several hundred in perfect conditions. The most common usage is to set --min-parallelism to a number higher than one to speed up scans of poorly performing hosts or networks. This is a risky option to play with, as setting it too high may affect accuracy. Setting this also reduces Nmap's ability to control parallelism dynamically based on network conditions. A value of 10 might be reasonable, though I only adjust this value as a last resort. The --max-parallelism option is sometimes set to one to prevent Nmap from sending more than one probe at a time to hosts. The --scan-delay option, discussed later, is another way to do this. --min-rtt-timeout time, --max-rtt-timeout time, --initial-rtt-timeout time (Adjust probe timeouts) Nmap maintains a running timeout value for determining how long it will wait for a probe response before giving up or retransmitting the probe. This is calculated based on the response times of previous probes. If the network latency shows itself to be significant and variable, this timeout can grow to several seconds. It also starts at a conservative (high) level and may stay that way for a while when Nmap scans unresponsive hosts. Specifying a lower --max-rtt-timeout and --initial-rtt-timeout than the defaults can cut scan times significantly. This is particularly true for pingless (-Pn) scans, and those against heavily filtered networks. Don't get too aggressive though. The scan can end up taking longer if you specify such a low value that many probes are timing out and retransmitting while the response is in transit. If all the hosts are on a local network, 100 milliseconds (--max-rtt-timeout 100ms) is a reasonable aggressive value. If routing is involved, ping a host on the network first with the ICMP ping utility, or with a custom packet crafter such as Nping that is more likely to get through a firewall. Look at the maximum round trip time out of ten packets or so. You might want to double that for the --initial-rtt-timeout and triple or quadruple it for the --max-rtt-timeout. I generally do not set the maximum RTT below 100 ms, no matter what the ping times are. Nor do I exceed 1000 ms. --min-rtt-timeout is a rarely used option that could be useful when a network is so unreliable that even Nmap's default is too aggressive. Since Nmap only reduces the timeout down to the minimum when the network seems to be reliable, this need is unusual and should be reported as a bug to the nmap-dev mailing list. --max-retries numtries (Specify the maximum number of port scan probe retransmissions) When Nmap receives no response to a port scan probe, it could mean the port is filtered. Or maybe the probe or response was simply lost on the network. It is also possible that the target host has rate limiting enabled that temporarily blocked the response. So Nmap tries again by retransmitting the initial probe. If Nmap detects poor network reliability, it may try many more times before giving up on a port. While this benefits accuracy, it also lengthens scan times. When performance is critical, scans may be sped up by limiting the number of retransmissions allowed. You can even specify --max-retries 0 to prevent any retransmissions, though that is only recommended for situations such as informal surveys where occasional missed ports and hosts are acceptable. The default (with no -T template) is to allow ten retransmissions. If a network seems reliable and the target hosts aren't rate limiting, Nmap usually only does one retransmission. So most target scans aren't even affected by dropping --max-retries to a low value such as three. Such values can substantially speed scans of slow (rate limited) hosts. You usually lose some information when Nmap gives up on ports early, though that may be preferable to letting the --host-timeout expire and losing all information about the target. --host-timeout time (Give up on slow target hosts) Some hosts simply take a long time to scan. This may be due to poorly performing or unreliable networking hardware or software, packet rate limiting, or a restrictive firewall. The slowest few percent of the scanned hosts can eat up a majority of the scan time. Sometimes it is best to cut your losses and skip those hosts initially. Specify --host-timeout with the maximum amount of time you are willing to wait. For example, specify 30m to ensure that Nmap doesn't waste more than half an hour on a single host. Note that Nmap may be scanning other hosts at the same time during that half an hour, so it isn't a complete loss. A host that times out is skipped. No port table, OS detection, or version detection results are printed for that host. The special value 0 can be used to mean “no timeout”, which can be used to override the T5 timing template, which sets the host timeout to 15 minutes. --script-timeout time While some scripts complete in fractions of a second, others can take hours or more depending on the nature of the script, arguments passed in, network and application conditions, and more. The --script-timeout option sets a ceiling on script execution time. Any script instance which exceeds that time will be terminated and no output will be shown. If debugging (-d) is enabled, Nmap will report on each timeout. For host and service scripts, a script instance only scans a single target host or port and the timeout period will be reset for the next instance. The special value 0 can be used to mean “no timeout”, which can be used to override the T5 timing template, which sets the script timeout to 10 minutes. --scan-delay time; --max-scan-delay time (Adjust delay between probes) This option causes Nmap to wait at least the given amount of time between each probe it sends to a given host. This is particularly useful in the case of rate limiting. Solaris machines (among many others) will usually respond to UDP scan probe packets with only one ICMP message per second. Any more than that sent by Nmap will be wasteful. A --scan-delay of 1s will keep Nmap at that slow rate. Nmap tries to detect rate limiting and adjust the scan delay accordingly, but it doesn't hurt to specify it explicitly if you already know what rate works best. When Nmap adjusts the scan delay upward to cope with rate limiting, the scan slows down dramatically. The --max-scan-delay option specifies the largest delay that Nmap will allow. A low --max-scan-delay can speed up Nmap, but it is risky. Setting this value too low can lead to wasteful packet retransmissions and possible missed ports when the target implements strict rate limiting. Another use of --scan-delay is to evade threshold based intrusion detection and prevention systems (IDS/IPS). --min-rate number; --max-rate number (Directly control the scanning rate) Nmap's dynamic timing does a good job of finding an appropriate speed at which to scan. Sometimes, however, you may happen to know an appropriate scanning rate for a network, or you may have to guarantee that a scan will be finished by a certain time. Or perhaps you must keep Nmap from scanning too quickly. The --min-rate and --max-rate options are designed for these situations. When the --min-rate option is given Nmap will do its best to send packets as fast as or faster than the given rate. The argument is a positive real number representing a packet rate in packets per second. For example, specifying --min-rate 300 means that Nmap will try to keep the sending rate at or above 300 packets per second. Specifying a minimum rate does not keep Nmap from going faster if conditions warrant. Likewise, --max-rate limits a scan's sending rate to a given maximum. Use --max-rate 100, for example, to limit sending to 100 packets per second on a fast network. Use --max-rate 0.1 for a slow scan of one packet every ten seconds. Use --min-rate and --max-rate together to keep the rate inside a certain range. These two options are global, affecting an entire scan, not individual hosts. They only affect port scans and host discovery scans. Other features like OS detection implement their own timing. There are two conditions when the actual scanning rate may fall below the requested minimum. The first is if the minimum is faster than the fastest rate at which Nmap can send, which is dependent on hardware. In this case Nmap will simply send packets as fast as possible, but be aware that such high rates are likely to cause a loss of accuracy. The second case is when Nmap has nothing to send, for example at the end of a scan when the last probes have been sent and Nmap is waiting for them to time out or be responded to. It's normal to see the scanning rate drop at the end of a scan or in between hostgroups. The sending rate may temporarily exceed the maximum to make up for unpredictable delays, but on average the rate will stay at or below the maximum. Specifying a minimum rate should be done with care. Scanning faster than a network can support may lead to a loss of accuracy. In some cases, using a faster rate can make a scan take longer than it would with a slower rate. This is because Nmap's adaptive retransmission algorithms will detect the network congestion caused by an excessive scanning rate and increase the number of retransmissions in order to improve accuracy. So even though packets are sent at a higher rate, more packets are sent overall. Cap the number of retransmissions with the --max-retries option if you need to set an upper limit on total scan time. --defeat-rst-ratelimit Many hosts have long used rate limiting to reduce the number of ICMP error messages (such as port-unreachable errors) they send. Some systems now apply similar rate limits to the RST (reset) packets they generate. This can slow Nmap down dramatically as it adjusts its timing to reflect those rate limits. You can tell Nmap to ignore those rate limits (for port scans such as SYN scan which don't treat non-responsive ports as open) by specifying --defeat-rst-ratelimit. Using this option can reduce accuracy, as some ports will appear non-responsive because Nmap didn't wait long enough for a rate-limited RST response. With a SYN scan, the non-response results in the port being labeled filtered rather than the closed state we see when RST packets are received. This option is useful when you only care about open ports, and distinguishing between closed and filtered ports isn't worth the extra time. --defeat-icmp-ratelimit Similar to --defeat-rst-ratelimit, the --defeat-icmp-ratelimit option trades accuracy for speed, increasing UDP scanning speed against hosts that rate-limit ICMP error messages. Because this option causes Nmap to not delay in order to receive the port unreachable messages, a non-responsive port will be labeled closed|filtered instead of the default open|filtered. This has the effect of only treating ports which actually respond via UDP as open. Since many UDP services do not respond in this way, the chance for inaccuracy is greater with this option than with --defeat-rst-ratelimit. --nsock-engine iocp|epoll|kqueue|poll|select Enforce use of a given nsock IO multiplexing engine. Only the select(2)-based fallback engine is guaranteed to be available on your system. Engines are named after the name of the IO management facility they leverage. Engines currently implemented are epoll, kqueue, poll, and select, but not all will be present on any platform. By default, Nmap will use the "best" engine, i.e. the first one in this list that is supported. Use nmap -V to see which engines are supported on your platform. -T paranoid|sneaky|polite|normal|aggressive|insane (Set a timing template) While the fine-grained timing controls discussed in the previous section are powerful and effective, some people find them confusing. Moreover, choosing the appropriate values can sometimes take more time than the scan you are trying to optimize. Fortunately, Nmap offers a simpler approach, with six timing templates. You can specify them with the -T option and their number (0–5) or their name. The template names are paranoid (0), sneaky (1), polite (2), normal (3), aggressive (4), and insane (5). The first two are for IDS evasion. Polite mode slows down the scan to use less bandwidth and target machine resources. Normal mode is the default and so -T3 does nothing. Aggressive mode speeds scans up by making the assumption that you are on a reasonably fast and reliable network. Finally insane mode assumes that you are on an extraordinarily fast network or are willing to sacrifice some accuracy for speed. These templates allow the user to specify how aggressive they wish to be, while leaving Nmap to pick the exact timing values. The templates also make some minor speed adjustments for which fine-grained control options do not currently exist. For example, -T4 prohibits the dynamic scan delay from exceeding 10 ms for TCP ports and -T5 caps that value at 5 ms. Templates can be used in combination with fine-grained controls, and the fine-grained controls that you specify will take precedence over the timing template default for that parameter. I recommend using -T4 when scanning reasonably modern and reliable networks. Keep that option even when you add fine-grained controls so that you benefit from those extra minor optimizations that it enables. If you are on a decent broadband or ethernet connection, I would recommend always using -T4. Some people love -T5 though it is too aggressive for my taste. People sometimes specify -T2 because they think it is less likely to crash hosts or because they consider themselves to be polite in general. They often don't realize just how slow -T polite really is. Their scan may take ten times longer than a default scan. Machine crashes and bandwidth problems are rare with the default timing options (-T3) and so I normally recommend that for cautious scanners. Omitting version detection is far more effective than playing with timing values at reducing these problems. While -T0 and -T1 may be useful for avoiding IDS alerts, they will take an extraordinarily long time to scan thousands of machines or ports. For such a long scan, you may prefer to set the exact timing values you need rather than rely on the canned -T0 and -T1 values. The main effects of T0 are serializing the scan so only one port is scanned at a time, and waiting five minutes between sending each probe. T1 and T2 are similar but they only wait 15 seconds and 0.4 seconds, respectively, between probes. T3 is Nmap's default behavior, which includes parallelization. -T4 does the equivalent of --max-rtt-timeout 1250ms --min-rtt-timeout 100ms --initial-rtt-timeout 500ms --max-retries 6 and sets the maximum TCP and SCTP scan delay to 10ms. T5 does the equivalent of --max-rtt-timeout 300ms --min-rtt-timeout 50ms --initial-rtt-timeout 250ms --max-retries 2 --host-timeout 15m --script-timeout 10m as well as setting the maximum TCP and SCTP scan delay to 5ms. Maximum UDP scan delay is not set by T4 or T5, but it can be set with the --max-scan-delay option. FIREWALL/IDS EVASION AND SPOOFING Many Internet pioneers envisioned a global open network with a universal IP address space allowing virtual connections between any two nodes. This allows hosts to act as true peers, serving and retrieving information from each other. People could access all of their home systems from work, changing the climate control settings or unlocking the doors for early guests. This vision of universal connectivity has been stifled by address space shortages and security concerns. In the early 1990s, organizations began deploying firewalls for the express purpose of reducing connectivity. Huge networks were cordoned off from the unfiltered Internet by application proxies, network address translation, and packet filters. The unrestricted flow of information gave way to tight regulation of approved communication channels and the content that passes over them. Network obstructions such as firewalls can make mapping a network exceedingly difficult. It will not get any easier, as stifling casual reconnaissance is often a key goal of implementing the devices. Nevertheless, Nmap offers many features to help understand these complex networks, and to verify that filters are working as intended. It even supports mechanisms for bypassing poorly implemented defenses. One of the best methods of understanding your network security posture is to try to defeat it. Place yourself in the mind-set of an attacker, and deploy techniques from this section against your networks. Launch an FTP bounce scan, idle scan, fragmentation attack, or try to tunnel through one of your own proxies. In addition to restricting network activity, companies are increasingly monitoring traffic with intrusion detection systems (IDS). All of the major IDSs ship with rules designed to detect Nmap scans because scans are sometimes a precursor to attacks. Many of these products have recently morphed into intrusion prevention systems (IPS) that actively block traffic deemed malicious. Unfortunately for network administrators and IDS vendors, reliably detecting bad intentions by analyzing packet data is a tough problem. Attackers with patience, skill, and the help of certain Nmap options can usually pass by IDSs undetected. Meanwhile, administrators must cope with large numbers of false positive results where innocent activity is misdiagnosed and alerted on or blocked. Occasionally people suggest that Nmap should not offer features for evading firewall rules or sneaking past IDSs. They argue that these features are just as likely to be misused by attackers as used by administrators to enhance security. The problem with this logic is that these methods would still be used by attackers, who would just find other tools or patch the functionality into Nmap. Meanwhile, administrators would find it that much harder to do their jobs. Deploying only modern, patched FTP servers is a far more powerful defense than trying to prevent the distribution of tools implementing the FTP bounce attack. There is no magic bullet (or Nmap option) for detecting and subverting firewalls and IDS systems. It takes skill and experience. A tutorial is beyond the scope of this reference guide, which only lists the relevant options and describes what they do. -f (fragment packets); --mtu (using the specified MTU) The -f option causes the requested scan (including host discovery scans) to use tiny fragmented IP packets. The idea is to split up the TCP header over several packets to make it harder for packet filters, intrusion detection systems, and other annoyances to detect what you are doing. Be careful with this! Some programs have trouble handling these tiny packets. The old-school sniffer named Sniffit segmentation faulted immediately upon receiving the first fragment. Specify this option once, and Nmap splits the packets into eight bytes or less after the IP header. So a 20-byte TCP header would be split into three packets. Two with eight bytes of the TCP header, and one with the final four. Of course each fragment also has an IP header. Specify -f again to use 16 bytes per fragment (reducing the number of fragments). Or you can specify your own offset size with the --mtu option. Don't also specify -f if you use --mtu. The offset must be a multiple of eight. While fragmented packets won't get by packet filters and firewalls that queue all IP fragments, such as the CONFIG_IP_ALWAYS_DEFRAG option in the Linux kernel, some networks can't afford the performance hit this causes and thus leave it disabled. Others can't enable this because fragments may take different routes into their networks. Some source systems defragment outgoing packets in the kernel. Linux with the iptables connection tracking module is one such example. Do a scan while a sniffer such as Wireshark is running to ensure that sent packets are fragmented. If your host OS is causing problems, try the --send-eth option to bypass the IP layer and send raw ethernet frames. Fragmentation is only supported for Nmap's raw packet features, which includes TCP and UDP port scans (except connect scan and FTP bounce scan) and OS detection. Features such as version detection and the Nmap Scripting Engine generally don't support fragmentation because they rely on your host's TCP stack to communicate with target services. -D decoy1[,decoy2][,ME][,...] (Cloak a scan with decoys) Causes a decoy scan to be performed, which makes it appear to the remote host that the host(s) you specify as decoys are scanning the target network too. Thus their IDS might report 5–10 port scans from unique IP addresses, but they won't know which IP was scanning them and which were innocent decoys. While this can be defeated through router path tracing, response-dropping, and other active mechanisms, it is generally an effective technique for hiding your IP address. Separate each decoy host with commas, and you can optionally use ME as one of the decoys to represent the position for your real IP address. If you put ME in the sixth position or later, some common port scan detectors (such as Solar Designer's excellent Scanlogd) are unlikely to show your IP address at all. If you don't use ME, Nmap will put you in a random position. You can also use RND to generate a random, non-reserved IP address, or RND:number to generate number addresses. Note that the hosts you use as decoys should be up or you might accidentally SYN flood your targets. Also it will be pretty easy to determine which host is scanning if only one is actually up on the network. You might want to use IP addresses instead of names (so the decoy networks don't see you in their nameserver logs). Right now random IP address generation is only supported with IPv4 Decoys are used both in the initial host discovery scan (using ICMP, SYN, ACK, or whatever) and during the actual port scanning phase. Decoys are also used during remote OS detection (-O). Decoys do not work with version detection or TCP connect scan. When a scan delay is in effect, the delay is enforced between each batch of spoofed probes, not between each individual probe. Because decoys are sent as a batch all at once, they may temporarily violate congestion control limits. It is worth noting that using too many decoys may slow your scan and potentially even make it less accurate. Also, some ISPs will filter out your spoofed packets, but many do not restrict spoofed IP packets at all. -S IP_Address (Spoof source address) In some circumstances, Nmap may not be able to determine your source address (Nmap will tell you if this is the case). In this situation, use -S with the IP address of the interface you wish to send packets through. Another possible use of this flag is to spoof the scan to make the targets think that someone else is scanning them. Imagine a company being repeatedly port scanned by a competitor! The -e option and -Pn are generally required for this sort of usage. Note that you usually won't receive reply packets back (they will be addressed to the IP you are spoofing), so Nmap won't produce useful reports. -e interface (Use specified interface) Tells Nmap what interface to send and receive packets on. Nmap should be able to detect this automatically, but it will tell you if it cannot. --source-port portnumber; -g portnumber (Spoof source port number) One surprisingly common misconfiguration is to trust traffic based only on the source port number. It is easy to understand how this comes about. An administrator will set up a shiny new firewall, only to be flooded with complaints from ungrateful users whose applications stopped working. In particular, DNS may be broken because the UDP DNS replies from external servers can no longer enter the network. FTP is another common example. In active FTP transfers, the remote server tries to establish a connection back to the client to transfer the requested file. Secure solutions to these problems exist, often in the form of application-level proxies or protocol-parsing firewall modules. Unfortunately there are also easier, insecure solutions. Noting that DNS replies come from port 53 and active FTP from port 20, many administrators have fallen into the trap of simply allowing incoming traffic from those ports. They often assume that no attacker would notice and exploit such firewall holes. In other cases, administrators consider this a short-term stop-gap measure until they can implement a more secure solution. Then they forget the security upgrade. Overworked network administrators are not the only ones to fall into this trap. Numerous products have shipped with these insecure rules. Even Microsoft has been guilty. The IPsec filters that shipped with Windows 2000 and Windows XP contain an implicit rule that allows all TCP or UDP traffic from port 88 (Kerberos). In another well-known case, versions of the Zone Alarm personal firewall up to 2.1.25 allowed any incoming UDP packets with the source port 53 (DNS) or 67 (DHCP). Nmap offers the -g and --source-port options (they are equivalent) to exploit these weaknesses. Simply provide a port number and Nmap will send packets from that port where possible. Most scanning operations that use raw sockets, including SYN and UDP scans, support the option completely. The option notably doesn't have an effect for any operations that use normal operating system sockets, including DNS requests, TCP connect scan, version detection, and script scanning. Setting the source port also doesn't work for OS detection, because Nmap must use different port numbers for certain OS detection tests to work properly. --data hex string (Append custom binary data to sent packets) This option lets you include binary data as payload in sent packets. hex string may be specified in any of the following formats: 0xAABBCCDDEEFF..., AABBCCDDEEFF... or \xAA\xBB\xCC\xDD\xEE\xFF.... Examples of use are --data 0xdeadbeef and --data \xCA\xFE\x09. Note that if you specify a number like 0x00ff no byte-order conversion is performed. Make sure you specify the information in the byte order expected by the receiver. --data-string string (Append custom string to sent packets) This option lets you include a regular string as payload in sent packets. string can contain any string. However, note that some characters may depend on your system's locale and the receiver may not see the same information. Also, make sure you enclose the string in double quotes and escape any special characters from the shell. Examples: --data-string "Scan conducted by Security Ops, extension 7192" or --data-string "Ph34r my l33t skills". Keep in mind that nobody is likely to actually see any comments left by this option unless they are carefully monitoring the network with a sniffer or custom IDS rules. --data-length number (Append random data to sent packets) Normally Nmap sends minimalist packets containing only a header. So its TCP packets are generally 40 bytes and ICMP echo requests are just 28. Some UDP ports and IP protocols get a custom payload by default. This option tells Nmap to append the given number of random bytes to most of the packets it sends, and not to use any protocol-specific payloads. (Use --data-length 0 for no random or protocol-specific payloads. OS detection (-O) packets are not affected because accuracy there requires probe consistency, but most pinging and portscan packets support this. It slows things down a little, but can make a scan slightly less conspicuous. --ip-options R|S [route]|L [route]|T|U ... ; --ip-options hex string (Send packets with specified ip options) The IP protocol[12] offers several options which may be placed in packet headers. Unlike the ubiquitous TCP options, IP options are rarely seen due to practicality and security concerns. In fact, many Internet routers block the most dangerous options such as source routing. Yet options can still be useful in some cases for determining and manipulating the network route to target machines. For example, you may be able to use the record route option to determine a path to a target even when more traditional traceroute-style approaches fail. Or if your packets are being dropped by a certain firewall, you may be able to specify a different route with the strict or loose source routing options. The most powerful way to specify IP options is to simply pass in values as the argument to --ip-options. Precede each hex number with \x then the two digits. You may repeat certain characters by following them with an asterisk and then the number of times you wish them to repeat. For example, \x01\x07\x04\x00*36\x01 is a hex string containing 36 NUL bytes. Nmap also offers a shortcut mechanism for specifying options. Simply pass the letter R, T, or U to request record-route, record-timestamp, or both options together, respectively. Loose or strict source routing may be specified with an L or S followed by a space and then a space-separated list of IP addresses. If you wish to see the options in packets sent and received, specify --packet-trace. For more information and examples of using IP options with Nmap, see https://seclists.org/nmap-dev/2006/q3/52. --ttl value (Set IP time-to-live field) Sets the IPv4 time-to-live field in sent packets to the given value. --randomize-hosts (Randomize target host order) Tells Nmap to shuffle each group of up to 16384 hosts before it scans them. This can make the scans less obvious to various network monitoring systems, especially when you combine it with slow timing options. If you want to randomize over larger group sizes, increase PING_GROUP_SZ in nmap.h and recompile. An alternative solution is to generate the target IP list with a list scan (-sL -n -oN filename), randomize it with a Perl script, then provide the whole list to Nmap with -iL. --spoof-mac MAC address, prefix, or vendor name (Spoof MAC address) Asks Nmap to use the given MAC address for all of the raw ethernet frames it sends. This option implies --send-eth to ensure that Nmap actually sends ethernet-level packets. The MAC given can take several formats. If it is simply the number 0, Nmap chooses a completely random MAC address for the session. If the given string is an even number of hex digits (with the pairs optionally separated by a colon), Nmap will use those as the MAC. If fewer than 12 hex digits are provided, Nmap fills in the remainder of the six bytes with random values. If the argument isn't a zero or hex string, Nmap looks through nmap-mac-prefixes to find a vendor name containing the given string (it is case insensitive). If a match is found, Nmap uses the vendor's OUI (three-byte prefix) and fills out the remaining three bytes randomly. Valid --spoof-mac argument examples are Apple, 0, 01:02:03:04:05:06, deadbeefcafe, 0020F2, and Cisco. This option only affects raw packet scans such as SYN scan or OS detection, not connection-oriented features such as version detection or the Nmap Scripting Engine. --proxies Comma-separated list of proxy URLs (Relay TCP connections through a chain of proxies) Asks Nmap to establish TCP connections with a final target through supplied chain of one or more HTTP or SOCKS4 proxies. Proxies can help hide the true source of a scan or evade certain firewall restrictions, but they can hamper scan performance by increasing latency. Users may need to adjust Nmap timeouts and other scan parameters accordingly. In particular, a lower --max-parallelism may help because some proxies refuse to handle as many concurrent connections as Nmap opens by default. This option takes a list of proxies as argument, expressed as URLs in the format proto://host:port. Use commas to separate node URLs in a chain. No authentication is supported yet. Valid protocols are HTTP and SOCKS4. Warning: this feature is still under development and has limitations. It is implemented within the nsock library and thus has no effect on the ping, port scanning and OS discovery phases of a scan. Only NSE and version scan benefit from this option so far—other features may disclose your true address. SSL connections are not yet supported, nor is proxy-side DNS resolution (hostnames are always resolved by Nmap). --badsum (Send packets with bogus TCP/UDP checksums) Asks Nmap to use an invalid TCP, UDP or SCTP checksum for packets sent to target hosts. Since virtually all host IP stacks properly drop these packets, any responses received are likely coming from a firewall or IDS that didn't bother to verify the checksum. For more details on this technique, see https://nmap.org/p60-12.html --adler32 (Use deprecated Adler32 instead of CRC32C for SCTP checksums) Asks Nmap to use the deprecated Adler32 algorithm for calculating the SCTP checksum. If --adler32 is not given, CRC-32C (Castagnoli) is used. RFC 2960[13] originally defined Adler32 as checksum algorithm for SCTP; RFC 4960[6] later redefined the SCTP checksums to use CRC-32C. Current SCTP implementations should be using CRC-32C, but in order to elicit responses from old, legacy SCTP implementations, it may be preferable to use Adler32. OUTPUT Any security tool is only as useful as the output it generates. Complex tests and algorithms are of little value if they aren't presented in an organized and comprehensible fashion. Given the number of ways Nmap is used by people and other software, no single format can please everyone. So Nmap offers several formats, including the interactive mode for humans to read directly and XML for easy parsing by software. In addition to offering different output formats, Nmap provides options for controlling the verbosity of output as well as debugging messages. Output types may be sent to standard output or to named files, which Nmap can append to or clobber. Output files may also be used to resume aborted scans. Nmap makes output available in five different formats. The default is called interactive output, and it is sent to standard output (stdout). There is also normal output, which is similar to interactive except that it displays less runtime information and warnings since it is expected to be analyzed after the scan completes rather than interactively. XML output is one of the most important output types, as it can be converted to HTML, easily parsed by programs such as Nmap graphical user interfaces, or imported into databases. The two remaining output types are the simple grepable output which includes most information for a target host on a single line, and sCRiPt KiDDi3 0utPUt for users who consider themselves |<-r4d. While interactive output is the default and has no associated command-line options, the other four format options use the same syntax. They take one argument, which is the filename that results should be stored in. Multiple formats may be specified, but each format may only be specified once. For example, you may wish to save normal output for your own review while saving XML of the same scan for programmatic analysis. You might do this with the options -oX myscan.xml -oN myscan.nmap. While this chapter uses the simple names like myscan.xml for brevity, more descriptive names are generally recommended. The names chosen are a matter of personal preference, though I use long ones that incorporate the scan date and a word or two describing the scan, placed in a directory named after the company I'm scanning. While these options save results to files, Nmap still prints interactive output to stdout as usual. For example, the command nmap -oX myscan.xml target prints XML to myscan.xml and fills standard output with the same interactive results it would have printed if -oX wasn't specified at all. You can change this by passing a hyphen character as the argument to one of the format types. This causes Nmap to deactivate interactive output, and instead print results in the format you specified to the standard output stream. So the command nmap -oX - target will send only XML output to stdout. Serious errors may still be printed to the normal error stream, stderr. Unlike some Nmap arguments, the space between the logfile option flag (such as -oX) and the filename or hyphen is mandatory. If you omit the flags and give arguments such as -oG- or -oXscan.xml, a backwards compatibility feature of Nmap will cause the creation of normal format output files named G- and Xscan.xml respectively. All of these arguments support strftime-like conversions in the filename. %H, %M, %S, %m, %d, %y, and %Y are all exactly the same as in strftime. %T is the same as %H%M%S, %R is the same as %H%M, and %D is the same as %m%d%y. A % followed by any other character just yields that character (%% gives you a percent symbol). So -oX 'scan-%T-%D.xml' will use an XML file with a name in the form of scan-144840-121307.xml. Nmap also offers options to control scan verbosity and to append to output files rather than clobbering them. All of these options are described below. Nmap Output Formats -oN filespec (normal output) Requests that normal output be directed to the given filename. As discussed above, this differs slightly from interactive output. -oX filespec (XML output) Requests that XML output be directed to the given filename. Nmap includes a document type definition (DTD) which allows XML parsers to validate Nmap XML output. While it is primarily intended for programmatic use, it can also help humans interpret Nmap XML output. The DTD defines the legal elements of the format, and often enumerates the attributes and values they can take on. The latest version is always available from https://svn.nmap.org/nmap/docs/nmap.dtd. XML offers a stable format that is easily parsed by software. Free XML parsers are available for all major computer languages, including C/C++, Perl, Python, and Java. People have even written bindings for most of these languages to handle Nmap output and execution specifically. Examples are Nmap::Scanner[14] and Nmap::Parser[15] in Perl CPAN. In almost all cases that a non-trivial application interfaces with Nmap, XML is the preferred format. The XML output references an XSL stylesheet which can be used to format the results as HTML. The easiest way to use this is simply to load the XML output in a web browser such as Firefox or IE. By default, this will only work on the machine you ran Nmap on (or a similarly configured one) due to the hard-coded nmap.xsl filesystem path. Use the --webxml or --stylesheet options to create portable XML files that render as HTML on any web-connected machine. -oS filespec (ScRipT KIdd|3 oUTpuT) Script kiddie output is like interactive output, except that it is post-processed to better suit the l33t HaXXorZ who previously looked down on Nmap due to its consistent capitalization and spelling. Humor impaired people should note that this option is making fun of the script kiddies before flaming me for supposedly “helping them”. -oG filespec (grepable output) This output format is covered last because it is deprecated. The XML output format is far more powerful, and is nearly as convenient for experienced users. XML is a standard for which dozens of excellent parsers are available, while grepable output is my own simple hack. XML is extensible to support new Nmap features as they are released, while I often must omit those features from grepable output for lack of a place to put them. Nevertheless, grepable output is still quite popular. It is a simple format that lists each host on one line and can be trivially searched and parsed with standard Unix tools such as grep, awk, cut, sed, diff, and Perl. Even I usually use it for one-off tests done at the command line. Finding all the hosts with the SSH port open or that are running Solaris takes only a simple grep to identify the hosts, piped to an awk or cut command to print the desired fields. Grepable output consists of comments (lines starting with a pound (#)) and target lines. A target line includes a combination of six labeled fields, separated by tabs and followed with a colon. The fields are Host, Ports, Protocols, Ignored State, OS, Seq Index, IP ID, and Status. The most important of these fields is generally Ports, which gives details on each interesting port. It is a comma separated list of port entries. Each port entry represents one interesting port, and takes the form of seven slash (/) separated subfields. Those subfields are: Port number, State, Protocol, Owner, Service, SunRPC info, and Version info. As with XML output, this man page does not allow for documenting the entire format. A more detailed look at the Nmap grepable output format is available from https://nmap.org/book/output-formats-grepable-output.html. -oA basename (Output to all formats) As a convenience, you may specify -oA basename to store scan results in normal, XML, and grepable formats at once. They are stored in basename.nmap, basename.xml, and basename.gnmap, respectively. As with most programs, you can prefix the filenames with a directory path, such as ~/nmaplogs/foocorp/ on Unix or c:\hacking\sco on Windows. Verbosity and debugging options -v (Increase verbosity level), -vlevel (Set verbosity level) Increases the verbosity level, causing Nmap to print more information about the scan in progress. Open ports are shown as they are found and completion time estimates are provided when Nmap thinks a scan will take more than a few minutes. Use it twice or more for even greater verbosity: -vv, or give a verbosity level directly, for example -v3. Most changes only affect interactive output, and some also affect normal and script kiddie output. The other output types are meant to be processed by machines, so Nmap can give substantial detail by default in those formats without fatiguing a human user. However, there are a few changes in other modes where output size can be reduced substantially by omitting some detail. For example, a comment line in the grepable output that provides a list of all ports scanned is only printed in verbose mode because it can be quite long. -d (Increase debugging level), -dlevel (Set debugging level) When even verbose mode doesn't provide sufficient data for you, debugging is available to flood you with much more! As with the verbosity option (-v), debugging is enabled with a command-line flag (-d) and the debug level can be increased by specifying it multiple times, as in -dd, or by setting a level directly. For example, -d9 sets level nine. That is the highest effective level and will produce thousands of lines unless you run a very simple scan with very few ports and targets. Debugging output is useful when a bug is suspected in Nmap, or if you are simply confused as to what Nmap is doing and why. As this feature is mostly intended for developers, debug lines aren't always self-explanatory. You may get something like: Timeout vals: srtt: -1 rttvar: -1 to: 1000000 delta 14987 ==> srtt: 14987 rttvar: 14987 to: 100000. If you don't understand a line, your only recourses are to ignore it, look it up in the source code, or request help from the development list (nmap-dev). Some lines are self explanatory, but the messages become more obscure as the debug level is increased. --reason (Host and port state reasons) Shows the reason each port is set to a specific state and the reason each host is up or down. This option displays the type of the packet that determined a port or hosts state. For example, A RST packet from a closed port or an echo reply from an alive host. The information Nmap can provide is determined by the type of scan or ping. The SYN scan and SYN ping (-sS and -PS) are very detailed, but the TCP connect scan (-sT) is limited by the implementation of the connect system call. This feature is automatically enabled by the debug option (-d) and the results are stored in XML log files even if this option is not specified. --stats-every time (Print periodic timing stats) Periodically prints a timing status message after each interval of time. The time is a specification of the kind described in the section called “TIMING AND PERFORMANCE”; so for example, use --stats-every 10s to get a status update every 10 seconds. Updates are printed to interactive output (the screen) and XML output. --packet-trace (Trace packets and data sent and received) Causes Nmap to print a summary of every packet sent or received. This is often used for debugging, but is also a valuable way for new users to understand exactly what Nmap is doing under the covers. To avoid printing thousands of lines, you may want to specify a limited number of ports to scan, such as -p20-30. If you only care about the goings on of the version detection subsystem, use --version-trace instead. If you only care about script tracing, specify --script-trace. With --packet-trace, you get all of the above. --open (Show only open (or possibly open) ports) Sometimes you only care about ports you can actually connect to (open ones), and don't want results cluttered with closed, filtered, and closed|filtered ports. Output customization is normally done after the scan using tools such as grep, awk, and Perl, but this feature was added due to overwhelming requests. Specify --open to only see hosts with at least one open, open|filtered, or unfiltered port, and only see ports in those states. These three states are treated just as they normally are, which means that open|filtered and unfiltered may be condensed into counts if there are an overwhelming number of them. Beginning with Nmap 7.40, the --open option implies --defeat-rst-ratelimit, because that option only affects closed and filtered ports, which are hidden by --open. --iflist (List interfaces and routes) Prints the interface list and system routes as detected by Nmap and quits. This is useful for debugging routing problems or device mischaracterization (such as Nmap treating a PPP connection as ethernet). Miscellaneous output options --append-output (Append to rather than clobber output files) When you specify a filename to an output format flag such as -oX or -oN, that file is overwritten by default. If you prefer to keep the existing content of the file and append the new results, specify the --append-output option. All output filenames specified in that Nmap execution will then be appended to rather than clobbered. This doesn't work well for XML (-oX) scan data as the resultant file generally won't parse properly until you fix it up by hand. --resume filename (Resume aborted scan) Some extensive Nmap runs take a very long time—on the order of days. Such scans don't always run to completion. Restrictions may prevent Nmap from being run during working hours, the network could go down, the machine Nmap is running on might suffer a planned or unplanned reboot, or Nmap itself could crash. The administrator running Nmap could cancel it for any other reason as well, by pressing ctrl-C. Restarting the whole scan from the beginning may be undesirable. Fortunately, if scan output files were kept, the user can ask Nmap to resume scanning with the target it was working on when execution ceased. Simply specify the --resume option and pass the output file as its argument. No other arguments are permitted, as Nmap parses the output file to use the same ones specified previously. Simply call Nmap as nmap --resume logfilename. Nmap will append new results to the data files specified in the previous execution. Scans can be resumed from any of the 3 major output formats: Normal, Grepable, or XML --noninteractive (Disable runtime interactions) At times, such as when running Nmap in a shell background, it might be undesirable for Nmap to monitor and respond to user keyboard input when running. (See the section called “RUNTIME INTERACTION” about how to control Nmap during a scan.) Use option --noninteractive to prevent Nmap taking control of the terminal. --stylesheet path or URL (Set XSL stylesheet to transform XML output) Nmap ships with an XSL stylesheet named nmap.xsl for viewing or translating XML output to HTML. The XML output includes an xml-stylesheet directive which points to nmap.xml where it was initially installed by Nmap. Run the XML file through an XSLT processor such as xsltproc[16] to produce an HTML file. Directly opening the XML file in a browser no longer works well because modern browsers limit the locations a stylesheet may be loaded from. If you wish to use a different stylesheet, specify it as the argument to --stylesheet. You must pass the full pathname or URL. One common invocation is --stylesheet https://nmap.org/svn/docs/nmap.xsl. This tells an XSLT processor to load the latest version of the stylesheet from Nmap.Org. The --webxml option does the same thing with less typing and memorization. Loading the XSL from Nmap.Org makes it easier to view results on a machine that doesn't have Nmap (and thus nmap.xsl) installed. So the URL is often more useful, but the local filesystem location of nmap.xsl is used by default for privacy reasons. --webxml (Load stylesheet from Nmap.Org) This is a convenience option, nothing more than an alias for --stylesheet https://nmap.org/svn/docs/nmap.xsl. --no-stylesheet (Omit XSL stylesheet declaration from XML) Specify this option to prevent Nmap from associating any XSL stylesheet with its XML output. The xml-stylesheet directive is omitted. MISCELLANEOUS OPTIONS This section describes some important (and not-so-important) options that don't really fit anywhere else. -6 (Enable IPv6 scanning) Nmap has IPv6 support for its most popular features. Ping scanning, port scanning, version detection, and the Nmap Scripting Engine all support IPv6. The command syntax is the same as usual except that you also add the -6 option. Of course, you must use IPv6 syntax if you specify an address rather than a hostname. An address might look like 3ffe:7501:4819:2000:210:f3ff:fe03:14d0, so hostnames are recommended. The output looks the same as usual, with the IPv6 address on the “interesting ports” line being the only IPv6 giveaway. While IPv6 hasn't exactly taken the world by storm, it gets significant use in some (usually Asian) countries and most modern operating systems support it. To use Nmap with IPv6, both the source and target of your scan must be configured for IPv6. If your ISP (like most of them) does not allocate IPv6 addresses to you, free tunnel brokers are widely available and work fine with Nmap. I use the free IPv6 tunnel broker service at http://www.tunnelbroker.net. Other tunnel brokers are listed at Wikipedia[17]. 6to4 tunnels are another popular, free approach. On Windows, raw-socket IPv6 scans are supported only on ethernet devices (not tunnels), and only on Windows Vista and later. Use the --unprivileged option in other situations. -A (Aggressive scan options) This option enables additional advanced and aggressive options. Presently this enables OS detection (-O), version scanning (-sV), script scanning (-sC) and traceroute (--traceroute). More features may be added in the future. The point is to enable a comprehensive set of scan options without people having to remember a large set of flags. However, because script scanning with the default set is considered intrusive, you should not use -A against target networks without permission. This option only enables features, and not timing options (such as -T4) or verbosity options (-v) that you might want as well. Options which require privileges (e.g. root access) such as OS detection and traceroute will only be enabled if those privileges are available. --datadir directoryname (Specify custom Nmap data file location) Nmap obtains some special data at runtime in files named nmap-service-probes, nmap-services, nmap-protocols, nmap-rpc, nmap-mac-prefixes, and nmap-os-db. If the location of any of these files has been specified (using the --servicedb or --versiondb options), that location is used for that file. After that, Nmap searches these files in the directory specified with the --datadir option (if any). Any files not found there, are searched for in the directory specified by the NMAPDIR environment variable. Next comes ~/.nmap for real and effective UIDs; or on Windows, HOME\AppData\Roaming\nmap (where HOME is the user's home directory, like C:\Users\user). This is followed by the location of the nmap executable and the same location with ../share/nmap appended. Then a compiled-in location such as /usr/local/share/nmap or /usr/share/nmap. --servicedb services file (Specify custom services file) Asks Nmap to use the specified services file rather than the nmap-services data file that comes with Nmap. Using this option also causes a fast scan (-F) to be used. See the description for --datadir for more information on Nmap's data files. --versiondb service probes file (Specify custom service probes file) Asks Nmap to use the specified service probes file rather than the nmap-service-probes data file that comes with Nmap. See the description for --datadir for more information on Nmap's data files. --send-eth (Use raw ethernet sending) Asks Nmap to send packets at the raw ethernet (data link) layer rather than the higher IP (network) layer. By default, Nmap chooses the one which is generally best for the platform it is running on. Raw sockets (IP layer) are generally most efficient for Unix machines, while ethernet frames are required for Windows operation since Microsoft disabled raw socket support. Nmap still uses raw IP packets on Unix despite this option when there is no other choice (such as non-ethernet connections). --send-ip (Send at raw IP level) Asks Nmap to send packets via raw IP sockets rather than sending lower level ethernet frames. It is the complement to the --send-eth option discussed previously. --privileged (Assume that the user is fully privileged) Tells Nmap to simply assume that it is privileged enough to perform raw socket sends, packet sniffing, and similar operations that usually require root privileges on Unix systems. By default Nmap quits if such operations are requested but geteuid is not zero. --privileged is useful with Linux kernel capabilities and similar systems that may be configured to allow unprivileged users to perform raw-packet scans. Be sure to provide this option flag before any flags for options that require privileges (SYN scan, OS detection, etc.). The NMAP_PRIVILEGED environment variable may be set as an equivalent alternative to --privileged. --unprivileged (Assume that the user lacks raw socket privileges) This option is the opposite of --privileged. It tells Nmap to treat the user as lacking network raw socket and sniffing privileges. This is useful for testing, debugging, or when the raw network functionality of your operating system is somehow broken. The NMAP_UNPRIVILEGED environment variable may be set as an equivalent alternative to --unprivileged. --release-memory (Release memory before quitting) This option is only useful for memory-leak debugging. It causes Nmap to release allocated memory just before it quits so that actual memory leaks are easier to spot. Normally Nmap skips this as the OS does this anyway upon process termination. -V; --version (Print version number) Prints the Nmap version number and exits. -h; --help (Print help summary page) Prints a short help screen with the most common command flags. Running Nmap without any arguments does the same thing. RUNTIME INTERACTION During the execution of Nmap, all key presses are captured. This allows you to interact with the program without aborting and restarting it. Certain special keys will change options, while any other keys will print out a status message telling you about the scan. The convention is that lowercase letters increase the amount of printing, and uppercase letters decrease the printing. You may also press ‘?’ for help. v / V Increase / decrease the verbosity level d / D Increase / decrease the debugging Level p / P Turn on / off packet tracing ? Print a runtime interaction help screen Anything else Print out a status message like this: Stats: 0:00:07 elapsed; 20 hosts completed (1 up), 1 undergoing Service Scan Service scan Timing: About 33.33% done; ETC: 20:57 (0:00:12 remaining) EXAMPLES Here are some Nmap usage examples, from the simple and routine to a little more complex and esoteric. Some actual IP addresses and domain names are used to make things more concrete. In their place you should substitute addresses/names from your own network. While I don't think port scanning other networks is or should be illegal, some network administrators don't appreciate unsolicited scanning of their networks and may complain. Getting permission first is the best approach. For testing purposes, you have permission to scan the host scanme.nmap.org. This permission only includes scanning via Nmap and not testing exploits or denial of service attacks. To conserve bandwidth, please do not initiate more than a dozen scans against that host per day. If this free scanning target service is abused, it will be taken down and Nmap will report Failed to resolve given hostname/IP: scanme.nmap.org. These permissions also apply to the hosts scanme2.nmap.org, scanme3.nmap.org, and so on, though those hosts do not currently exist. nmap -v scanme.nmap.org This option scans all reserved TCP ports on the machine scanme.nmap.org . The -v option enables verbose mode. nmap -sS -O scanme.nmap.org/24 Launches a stealth SYN scan against each machine that is up out of the 256 IPs on the /24 sized network where Scanme resides. It also tries to determine what operating system is running on each host that is up and running. This requires root privileges because of the SYN scan and OS detection. nmap -sV -p 22,53,110,143,4564 198.116.0-255.1-127 Launches host enumeration and a TCP scan at the first half of each of the 255 possible eight-bit subnets in the 198.116.0.0/16 address space. This tests whether the systems run SSH, DNS, POP3, or IMAP on their standard ports, or anything on port 4564. For any of these ports found open, version detection is used to determine what application is running. nmap -v -iR 100000 -Pn -p 80 Asks Nmap to choose 100,000 hosts at random and scan them for web servers (port 80). Host enumeration is disabled with -Pn since first sending a couple probes to determine whether a host is up is wasteful when you are only probing one port on each target host anyway. nmap -Pn -p80 -oX logs/pb-port80scan.xml -oG logs/pb-port80scan.gnmap 216.163.128.20/20 This scans 4096 IPs for any web servers (without pinging them) and saves the output in grepable and XML formats. NMAP BOOK While this reference guide details all material Nmap options, it can't fully demonstrate how to apply those features to quickly solve real-world tasks. For that, we released Nmap Network Scanning: The Official Nmap Project Guide to Network Discovery and Security Scanning. Topics include subverting firewalls and intrusion detection systems, optimizing Nmap performance, and automating common networking tasks with the Nmap Scripting Engine. Hints and instructions are provided for common Nmap tasks such as taking network inventory, penetration testing, detecting rogue wireless access points, and quashing network worm outbreaks. Examples and diagrams show actual communication on the wire. More than half of the book is available free online. See https://nmap.org/book for more information. BUGS Like its author, Nmap isn't perfect. But you can help make it better by sending bug reports or even writing patches. If Nmap doesn't behave the way you expect, first upgrade to the latest version available from https://nmap.org. If the problem persists, do some research to determine whether it has already been discovered and addressed. Try searching for the problem or error message on Google since that aggregates so many forums. If nothing comes of this, create an Issue on our tracker (http://issues.nmap.org) and/or mail a bug report to <dev@nmap.org>. If you subscribe to the nmap-dev list before posting, your message will bypass moderation and get through more quickly. Subscribe at https://nmap.org/mailman/listinfo/dev. Please include everything you have learned about the problem, as well as what version of Nmap you are using and what operating system version it is running on. Other suggestions for improving Nmap may be sent to the Nmap dev mailing list as well. If you are able to write a patch improving Nmap or fixing a bug, that is even better! Instructions for submitting patches or git pull requests are available from https://github.com/nmap/nmap/blob/master/CONTRIBUTING.md Particularly sensitive issues such as a security reports may be sent directly to Nmap's author Fyodor directly at <fyodor@nmap.org>. All other reports and comments should use the dev list or issue tracker instead because more people read, follow, and respond to those. AUTHORS Gordon “Fyodor” Lyon <fyodor@nmap.org> wrote and released Nmap in 1997. Since then, hundreds of people have made valuable contributions, as detailed in the CHANGELOG file distributed with Nmap and also available from https://nmap.org/changelog.html. David Fifield and Daniel Miller deserve special recognition for their enormous multi-year contributions! LEGAL NOTICES Nmap Copyright and Licensing The Nmap Security Scanner is (C) 1996–2022 Nmap Software LLC ("The Nmap Project"). Nmap is also a registered trademark of the Nmap Project. It is published under the Nmap Public Source License[18]. This generally allows end users to download and use Nmap for free. It doesn't allow Nmap to be used and redistributed within commercial software or hardware products (including appliances, virtual machines, and traditional applications). We fund the project by selling a special Nmap OEM Edition for this purpose, as described at https://nmap.org/oem. Hundreds of large and small software vendors have already purchased OEM licenses to embed Nmap technology such as host discovery, port scanning, OS detection, version detection, and the Nmap Scripting Engine within their products. The Nmap Project has permission to redistribute Npcap, a packet capturing driver and library for the Microsoft Windows platform. Npcap is a separate work with it's own license rather than this Nmap license. Since the Npcap license does not permit redistribution without special permission, our Nmap Windows binary packages which contain Npcap may not be redistributed without special permission. Even though the NPSL is based on GPLv2, it contains different provisions and is not directly compatible. It is incompatible with some other open source licenses as well. In some cases we can relicense portions of Nmap or grant special permissions to use it in other open source software. Please contact fyodor@nmap.org with any such requests. Similarly, we don't incorporate incompatible open source software into Nmap without special permission from the copyright holders. If you have received a written license agreement or contract for Nmap (such as an Nmap OEM license[19]) stating terms other than these, you may choose to use and redistribute Nmap under those terms instead. Creative Commons License for this Nmap Guide This Nmap Reference Guide is (C) 2005–2022 Nmap Software LLC. It is hereby placed under version 3.0 of the Creative Commons Attribution License[20]. This allows you redistribute and modify the work as you desire, as long as you credit the original source. Alternatively, you may choose to treat this document as falling under the same license as Nmap itself (discussed previously). Source Code Availability and Community Contributions Source is provided to this software because we believe users have a right to know exactly what a program is going to do before they run it. This also allows you to audit the software for security holes. Source code also allows you to port Nmap to new platforms, fix bugs, and add new features. You are highly encouraged to submit your changes as Github Pull Requests (PR) or send them to <dev@nmap.org> for possible incorporation into the main distribution. By submitting such changes, it is assumed that you are offering the Nmap Project the unlimited, non-exclusive right to reuse, modify, and relicense the code. This is important because the inability to relicense code has caused devastating problems for other Free Software projects (such as KDE and NASM). We also sell commercial licenses to Nmap OEM[21]. If you wish to specify special license conditions of your contributions, just say so when you send them. No Warranty This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. It should also be noted that Nmap has occasionally been known to crash poorly written applications, TCP/IP stacks, and even operating systems. While this is extremely rare, it is important to keep in mind. Nmap should never be run against mission critical systems unless you are prepared to suffer downtime. We acknowledge here that Nmap may crash your systems or networks and we disclaim all liability for any damage or problems Nmap could cause. Inappropriate Usage Because of the slight risk of crashes and because a few black hats like to use Nmap for reconnaissance prior to attacking systems, there are administrators who become upset and may complain when their system is scanned. Thus, it is often advisable to request permission before doing even a light scan of a network. Nmap should never be installed with special privileges (e.g. suid root). That would open up a major security vulnerability as other users on the system (or attackers) could use it for privilege escalation. Nmap is not designed, manufactured, or intended for use in hazardous environments requiring fail- safe performance where the failure of the software could lead directly to death, personal injury, or significant physical or environmental damage. Third-Party Software and Funding Notices This product includes software developed by the Apache Software Foundation[22]. A modified version of the Libpcap portable packet capture library[23] is distributed along with Nmap. The Windows version of Nmap utilizes the Libpcap-derived Ncap library[24] instead. Regular expression support is provided by the PCRE library[25], which is open-source software, written by Philip Hazel. Certain raw networking functions use the Libdnet[26] networking library, which was written by Dug Song. A modified version is distributed with Nmap. Nmap can optionally link with the OpenSSL cryptography toolkit[27] for SSL version detection support. The Nmap Scripting Engine uses an embedded version of the Lua programming language[10]. The Liblinear linear classification library[28] is used for our IPv6 OS detection machine learning techniques[29]. All of the third-party software described in this paragraph is freely redistributable under BSD-style software licenses. Binary packages for Windows and Mac OS X include support libraries necessary to run Zenmap and Ndiff with Python and PyGTK. (Unix platforms commonly make these libraries easy to install, so they are not part of the packages.) A listing of these support libraries and their licenses is included in the LICENSES files. This software was supported in part through the Google Summer of Code[30] and the DARPA CINDER program[31] (DARPA-BAA-10-84). United States Export Control Nmap only uses encryption when compiled with the optional OpenSSL support and linked with OpenSSL. When compiled without OpenSSL support, the Nmap Project believes that Nmap is not subject to U.S. Export Administration Regulations (EAR)[32] export control. As such, there is no applicable ECCN (export control classification number) and exportation does not require any special license, permit, or other governmental authorization. When compiled with OpenSSL support or distributed as source code, the Nmap Project believes that Nmap falls under U.S. ECCN 5D002[33] (“Information Security Software”). We distribute Nmap under the TSU exception for publicly available encryption software defined in EAR 740.13(e)[34]. NOTES 1. Nmap Network Scanning: The Official Nmap Project Guide to Network Discovery and Security Scanning https://nmap.org/book/ 2. RFC 1122 http://www.rfc-editor.org/rfc/rfc1122.txt 3. RFC 792 http://www.rfc-editor.org/rfc/rfc792.txt 4. RFC 950 http://www.rfc-editor.org/rfc/rfc950.txt 5. UDP http://www.rfc-editor.org/rfc/rfc768.txt 6. SCTP http://www.rfc-editor.org/rfc/rfc4960.txt 7. TCP RFC http://www.rfc-editor.org/rfc/rfc793.txt 8. RFC 959 http://www.rfc-editor.org/rfc/rfc959.txt 9. RFC 1323 http://www.rfc-editor.org/rfc/rfc1323.txt 10. Lua programming language https://lua.org 11. precedence http://www.lua.org/manual/5.4/manual.html#3.4.8 12. IP protocol http://www.rfc-editor.org/rfc/rfc791.txt 13. RFC 2960 http://www.rfc-editor.org/rfc/rfc2960.txt 14. Nmap::Scanner http://sourceforge.net/projects/nmap-scanner/ 15. Nmap::Parser http://nmapparser.wordpress.com/ 16. xsltproc http://xmlsoft.org/XSLT/ 17. listed at Wikipedia http://en.wikipedia.org/wiki/List_of_IPv6_tunnel_brokers 18. Nmap Public Source License https://nmap.org/npsl 19. Nmap OEM license https://nmap.org/oem/ 20. Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0/ 21. Nmap OEM https://nmap.org/oem 22. Apache Software Foundation https://www.apache.org 23. Libpcap portable packet capture library https://www.tcpdump.org 24. Ncap library https://npcap.com 25. PCRE library https://pcre.org 26. Libdnet http://libdnet.sourceforge.net 27. OpenSSL cryptography toolkit https://openssl.org 28. Liblinear linear classification library https://www.csie.ntu.edu.tw/~cjlin/liblinear/ 29. IPv6 OS detection machine learning techniques https://nmap.org/book/osdetect-guess.html#osdetect-guess-ipv6 30. Google Summer of Code https://nmap.org/soc/ 31. DARPA CINDER program https://www.fbo.gov/index?s=opportunity&mode=form&id=585e02a51f77af5cb3c9e06b9cc82c48&tab=core&_cview=1 32. Export Administration Regulations (EAR) https://www.bis.doc.gov/index.php/regulations/export-administration-regulations-ear 33. 5D002 https://www.bis.doc.gov/index.php/documents/regulations-docs/federal-register-notices/federal-register-2014/951-ccl5-pt2/file 34. EAR 740.13(e) https://www.bis.doc.gov/index.php/documents/regulations-docs/2341-740-2/file Nmap 05/17/2023 NMAP(1)
getent コマンドメモ
手元の getent version $ getent --version getent (Ubuntu GLIBC 2.39-0ubuntu8.6) 2.39 Copyright (C) 2024 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. Written by Thorsten Kukuk. man より引用 getent(1) General Commands Manual getent(1) NAME getent - get entries from Name Service Switch libraries SYNOPSIS getent [option]... database key... DESCRIPTION The getent command displays entries from databases supported by the Name Service Switch libraries, which are configured in /etc/nsswitch.conf. If one or more key arguments are provided, then only the entries that match the supplied keys will be displayed. Otherwise, if no key is provided, all entries will be displayed (unless the database does not support enumeration). The database may be any of those supported by the GNU C Library, listed below: ahosts When no key is provided, use sethostent(3), gethostent(3), and endhostent(3) to enumerate the hosts database. This is identical to using hosts(5). When one or more key arguments are provided, pass each key in succession to getaddrinfo(3) with the address family AF_UNSPEC, enu‐ merating each socket address structure returned. ahostsv4 Same as ahosts, but use the address family AF_INET. ahostsv6 Same as ahosts, but use the address family AF_INET6. The call to getaddrinfo(3) in this case includes the AI_V4MAPPED flag. aliases When no key is provided, use setaliasent(3), getaliasent(3), and endaliasent(3) to enumerate the aliases database. When one or more key argu‐ ments are provided, pass each key in succession to getaliasbyname(3) and display the result. ethers When one or more key arguments are provided, pass each key in succession to ether_aton(3) and ether_hostton(3) until a result is obtained, and display the result. Enumeration is not supported on ethers, so a key must be provided. group When no key is provided, use setgrent(3), getgrent(3), and endgrent(3) to enumerate the group database. When one or more key arguments are provided, pass each numeric key to getgrgid(3) and each nonnumeric key to getgrnam(3) and display the result. gshadow When no key is provided, use setsgent(3), getsgent(3), and endsgent(3) to enumerate the gshadow database. When one or more key arguments are provided, pass each key in succession to getsgnam(3) and display the result. hosts When no key is provided, use sethostent(3), gethostent(3), and endhostent(3) to enumerate the hosts database. When one or more key arguments are provided, pass each key to gethostbyaddr(3) or gethostbyname2(3), depending on whether a call to inet_pton(3) indicates that the key is an IPv6 or IPv4 address or not, and display the result. initgroups When one or more key arguments are provided, pass each key in succession to getgrouplist(3) and display the result. Enumeration is not sup‐ ported on initgroups, so a key must be provided. netgroup When one key is provided, pass the key to setnetgrent(3) and, using getnetgrent(3) display the resulting string triple (hostname, username, domainname). Alternatively, three keys may be provided, which are interpreted as the hostname, username, and domainname to match to a net‐ group name via innetgr(3). Enumeration is not supported on netgroup, so either one or three keys must be provided. networks When no key is provided, use setnetent(3), getnetent(3), and endnetent(3) to enumerate the networks database. When one or more key arguments are provided, pass each numeric key to getnetbyaddr(3) and each nonnumeric key to getnetbyname(3) and display the result. passwd When no key is provided, use setpwent(3), getpwent(3), and endpwent(3) to enumerate the passwd database. When one or more key arguments are provided, pass each numeric key to getpwuid(3) and each nonnumeric key to getpwnam(3) and display the result. protocols When no key is provided, use setprotoent(3), getprotoent(3), and endprotoent(3) to enumerate the protocols database. When one or more key ar‐ guments are provided, pass each numeric key to getprotobynumber(3) and each nonnumeric key to getprotobyname(3) and display the result. rpc When no key is provided, use setrpcent(3), getrpcent(3), and endrpcent(3) to enumerate the rpc database. When one or more key arguments are provided, pass each numeric key to getrpcbynumber(3) and each nonnumeric key to getrpcbyname(3) and display the result. services When no key is provided, use setservent(3), getservent(3), and endservent(3) to enumerate the services database. When one or more key argu‐ ments are provided, pass each numeric key to getservbynumber(3) and each nonnumeric key to getservbyname(3) and display the result. shadow When no key is provided, use setspent(3), getspent(3), and endspent(3) to enumerate the shadow database. When one or more key arguments are provided, pass each key in succession to getspnam(3) and display the result. OPTIONS --service service -s service Override all databases with the specified service. (Since glibc 2.2.5.) --service database:service -s database:service Override only specified databases with the specified service. The option may be used multiple times, but only the last service for each data‐ base will be used. (Since glibc 2.4.) --no-idn -i Disables IDN encoding in lookups for ahosts/getaddrinfo(3) (Since glibc-2.13.) --help -? Print a usage summary and exit. --usage Print a short usage summary and exit. --version -V Print the version number, license, and disclaimer of warranty for getent. EXIT STATUS One of the following exit values can be returned by getent: 0 Command completed successfully. 1 Missing arguments, or database unknown. 2 One or more supplied key could not be found in the database. 3 Enumeration not supported on this database. SEE ALSO nsswitch.conf(5) Linux man-pages 6.7 2023-11-01 getent(1)
getaddrinfoメモ
はじめに curl google.com やChromeでgoogle.comへアクセスする際など、アプリケーションがドメイン名を利用しようとするとき、内部的にはC標準ライブラリのgetaddrinfoにこのドメイン名が渡されて、IPアドレスに解決されている。 この際の挙動をいつも忘れるのでメモする。 本文 概要 ドメイン名を渡したりIPアドレスを渡したりすると、様々な設定を用いて、そのドメイン名やIPアドレスが対応するIPアドレスを1つ以上返してくれる。 基本的な使い方 インターフェース int getaddrinfo(const char *restrict node, const char *restrict service, const struct addrinfo *restrict hints, struct addrinfo **restrict res); 実際の値のイメージ node = "google.com" service = "http" フローのイメージ curl google.com が呼ばれる ダイナミックリンクされている、libc.soのgetaddrinfo(“google.com”, “http”)が呼ばれる libresolv が呼ばれる libresolv が、/etc/nsswitch.confを読み込む(備考のように書かれていたとする) まずfiles、すなわち/etc/hostsで解決が試みられる 次にresolve、すなわちsystemd-resolvedで解決が試みられる。具体的には、ネットワークインターフェースごとにドメインが設定してあるので、そのドメインに該当した場合はそのインターフェースに設定されたDNSのIPアドレスにドメイン解決クエリを発行する。 dns、すなわち/etc/resolv.confに記載されたDNSのIPアドレスにドメイン解決クエリを発行する。備考の場合、127.0.0.53である。 備考1 /etc/nsswitch.conf hosts: files resolve dns 備考2 全体的に未検証だが、systemd-resolvedにおいては、ネットワークインターフェースごとでなく、全体のフォールバックとしてのDNSサーバのIPアドレスを設定できる。そのため、resolveが設定されていれば、その後ろにdnsは置かなくてよいらしい。 備考3 /etc/resolv.conf nameserver 127.0.0.53
riscv64-unknown-elf-objdumpコマンドメモ
はじめに RiscVの学習でよく使うようになったのでメモ help Usage: riscv64-unknown-elf-objdump <option(s)> <file(s)> Display information from object <file(s)>. At least one of the following switches must be given: -a, --archive-headers Display archive header information -f, --file-headers Display the contents of the overall file header -p, --private-headers Display object format specific file header contents -P, --private=OPT,OPT... Display object format specific contents -h, --[section-]headers Display the contents of the section headers -x, --all-headers Display the contents of all headers -d, --disassemble Display assembler contents of executable sections -D, --disassemble-all Display assembler contents of all sections --disassemble=<sym> Display assembler contents from <sym> -S, --source Intermix source code with disassembly --source-comment[=<txt>] Prefix lines of source code with <txt> -s, --full-contents Display the full contents of all sections requested -Z, --decompress Decompress section(s) before displaying their contents -g, --debugging Display debug information in object file -e, --debugging-tags Display debug information using ctags style -G, --stabs Display (in raw form) any STABS info in the file -W, --dwarf[a/=abbrev, A/=addr, r/=aranges, c/=cu_index, L/=decodedline, f/=frames, F/=frames-interp, g/=gdb_index, i/=info, o/=loc, m/=macro, p/=pubnames, t/=pubtypes, R/=Ranges, l/=rawline, s/=str, O/=str-offsets, u/=trace_abbrev, T/=trace_aranges, U/=trace_info] Display the contents of DWARF debug sections -Wk,--dwarf=links Display the contents of sections that link to separate debuginfo files -WK,--dwarf=follow-links Follow links to separate debug info files (default) -WN,--dwarf=no-follow-links Do not follow links to separate debug info files -L, --process-links Display the contents of non-debug sections in separate debuginfo files. (Implies -WK) --ctf[=SECTION] Display CTF info from SECTION, (default `.ctf') --sframe[=SECTION] Display SFrame info from SECTION, (default '.sframe') -t, --syms Display the contents of the symbol table(s) -T, --dynamic-syms Display the contents of the dynamic symbol table -r, --reloc Display the relocation entries in the file -R, --dynamic-reloc Display the dynamic relocation entries in the file @<file> Read options from <file> -v, --version Display this program's version number -i, --info List object formats and architectures supported -H, --help Display this information The following switches are optional: -b, --target=BFDNAME Specify the target object format as BFDNAME -m, --architecture=MACHINE Specify the target architecture as MACHINE -j, --section=NAME Only display information for section NAME -M, --disassembler-options=OPT Pass text OPT on to the disassembler -EB --endian=big Assume big endian format when disassembling -EL --endian=little Assume little endian format when disassembling --file-start-context Include context from start of file (with -S) -I, --include=DIR Add DIR to search list for source files -l, --line-numbers Include line numbers and filenames in output -F, --file-offsets Include file offsets when displaying information -C, --demangle[=STYLE] Decode mangled/processed symbol names STYLE can be "none", "auto", "gnu-v3", "java", "gnat", "dlang", "rust" --recurse-limit Enable a limit on recursion whilst demangling (default) --no-recurse-limit Disable a limit on recursion whilst demangling -w, --wide Format output for more than 80 columns -U[d|l|i|x|e|h] Controls the display of UTF-8 unicode characters --unicode=[default|locale|invalid|hex|escape|highlight] -z, --disassemble-zeroes Do not skip blocks of zeroes when disassembling --start-address=ADDR Only process data whose address is >= ADDR --stop-address=ADDR Only process data whose address is < ADDR --no-addresses Do not print address alongside disassembly --prefix-addresses Print complete address alongside disassembly --[no-]show-raw-insn Display hex alongside symbolic disassembly --insn-width=WIDTH Display WIDTH bytes on a single line for -d --adjust-vma=OFFSET Add OFFSET to all displayed section addresses --show-all-symbols When disassembling, display all symbols at a given address --special-syms Include special symbols in symbol dumps --inlines Print all inlines for source line (with -l) --prefix=PREFIX Add PREFIX to absolute paths for -S --prefix-strip=LEVEL Strip initial directory names for -S --dwarf-depth=N Do not display DIEs at depth N or greater --dwarf-start=N Display DIEs starting at offset N --dwarf-check Make additional dwarf consistency checks. --ctf-parent=NAME Use CTF archive member NAME as the CTF parent --visualize-jumps Visualize jumps by drawing ASCII art lines --visualize-jumps=color Use colors in the ASCII art --visualize-jumps=extended-color Use extended 8-bit color codes --visualize-jumps=off Disable jump visualization --disassembler-color=off Disable disassembler color output. (default) --disassembler-color=terminal Enable disassembler color output if displaying on a terminal. --disassembler-color=on Enable disassembler color output. --disassembler-color=extended Use 8-bit colors in disassembler output. riscv64-unknown-elf-objdump: supported targets: elf64-littleriscv elf32-littleriscv elf32-bigriscv elf64-bigriscv pei-riscv64-little elf64-little elf64-big elf32-little elf32-big srec symbolsrec verilog tekhex binary ihex plugin riscv64-unknown-elf-objdump: supported architectures: riscv riscv:rv64 riscv:rv32 The following RISC-V specific disassembler options are supported for use with the -M switch (multiple options should be separated by commas): numeric Print numeric register names, rather than ABI names. no-aliases Disassemble only into canonical instructions. priv-spec=SPEC Print the CSR according to the chosen privilege spec. For the options above, the following values are supported for "SPEC": 1.9.1 1.10 1.11 1.12 Report bugs to <https://sourceware.org/bugzilla/>. man objdump と同じだったので省略 ...
objdumpコマンドメモ
はじめに 最近、使うようになったのでmanをメモ man objdump より引用 OBJDUMP(1) GNU Development Tools OBJDUMP(1) NAME objdump - display information from object files SYNOPSIS objdump [-a|--archive-headers] [-b bfdname|--target=bfdname] [-C|--demangle[=style] ] [-d|--disassemble[=symbol]] [-D|--disassemble-all] [-z|--disassemble-zeroes] [-EB|-EL|--endian={big | little }] [-f|--file-headers] [-F|--file-offsets] [--file-start-context] [-g|--debugging] [-e|--debugging-tags] [-h|--section-headers|--headers] [-i|--info] [-j section|--section=section] [-l|--line-numbers] [-S|--source] [--source-comment[=text]] [-m machine|--architecture=machine] [-M options|--disassembler-options=options] [-p|--private-headers] [-P options|--private=options] [-r|--reloc] [-R|--dynamic-reloc] [-s|--full-contents] [-Z|--decompress] [-W[lLiaprmfFsoORtUuTgAck]| --dwarf[=rawline,=decodedline,=info,=abbrev,=pubnames,=aranges,=macro,=frames,=frames-interp,=str,=str-offsets,=loc,=Ranges,=pubtypes,=trace_info,=trace_abbrev,=trace_aranges,=gdb_index,=addr,=cu_index,=links]] [-WK|--dwarf=follow-links] [-WN|--dwarf=no-follow-links] [-wD|--dwarf=use-debuginfod] [-wE|--dwarf=do-not-use-debuginfod] [-L|--process-links] [--ctf=section] [--sframe=section] [-G|--stabs] [-t|--syms] [-T|--dynamic-syms] [-x|--all-headers] [-w|--wide] [--start-address=address] [--stop-address=address] [--no-addresses] [--prefix-addresses] [--[no-]show-raw-insn] [--adjust-vma=offset] [--show-all-symbols] [--dwarf-depth=n] [--dwarf-start=n] [--ctf-parent=section] [--no-recurse-limit|--recurse-limit] [--special-syms] [--prefix=prefix] [--prefix-strip=level] [--insn-width=width] [--visualize-jumps[=color|=extended-color|=off] [--disassembler-color=[off|terminal|on|extended] [-U method] [--unicode=method] [-V|--version] [-H|--help] objfile... DESCRIPTION objdump displays information about one or more object files. The options control what particular information to display. This information is mostly useful to programmers who are working on the compilation tools, as opposed to programmers who just want their program to compile and work. objfile... are the object files to be examined. When you specify archives, objdump shows information on each of the member object files. OPTIONS The long and short forms of options, shown here as alternatives, are equivalent. At least one option from the list -a,-d,-D,-e,-f,-g,-G,-h,-H,-p,-P,-r,-R,-s,-S,-t,-T,-V,-x must be given. -a --archive-header If any of the objfile files are archives, display the archive header information (in a format similar to ls -l). Besides the information you could list with ar tv, objdump -a shows the object file format of each archive member. --adjust-vma=offset When dumping information, first add offset to all the section addresses. This is useful if the section addresses do not correspond to the symbol table, which can happen when putting sections at particular addresses when using a format which can not represent section addresses, such as a.out. -b bfdname --target=bfdname Specify that the object-code format for the object files is bfdname. This option may not be necessary; objdump can automatically recognize many formats. For example, objdump -b oasys -m vax -h fu.o displays summary information from the section headers (-h) of fu.o, which is explicitly identified (-m) as a VAX object file in the format produced by Oasys compilers. You can list the formats available with the -i option. -C --demangle[=style] Decode (demangle) low-level symbol names into user-level names. Besides removing any initial underscore prepended by the system, this makes C++ function names readable. Different compilers have different mangling styles. The optional demangling style argument can be used to choose an appropriate demangling style for your compiler. --recurse-limit --no-recurse-limit --recursion-limit --no-recursion-limit Enables or disables a limit on the amount of recursion performed whilst demangling strings. Since the name mangling formats allow for an infinite level of recursion it is possible to create strings whose decoding will exhaust the amount of stack space available on the host machine, triggering a memory fault. The limit tries to prevent this from happening by restricting recursion to 2048 levels of nesting. The default is for this limit to be enabled, but disabling it may be necessary in order to demangle truly complicated names. Note however that if the recursion limit is disabled then stack exhaustion is possible and any bug reports about such an event will be rejected. -g --debugging Display debugging information. This attempts to parse STABS debugging format information stored in the file and print it out using a C like syntax. If no STABS debugging was found this option falls back on the -W option to print any DWARF information in the file. -e --debugging-tags Like -g, but the information is generated in a format compatible with ctags tool. -d --disassemble --disassemble=symbol Display the assembler mnemonics for the machine instructions from the input file. This option only disassembles those sections which are expected to contain instructions. If the optional symbol argument is given, then display the assembler mnemonics starting at symbol. If symbol is a function name then disassembly will stop at the end of the function, otherwise it will stop when the next symbol is encountered. If there are no matches for symbol then nothing will be displayed. Note if the --dwarf=follow-links option is enabled then any symbol tables in linked debug info files will be read in and used when disassembling. -D --disassemble-all Like -d, but disassemble the contents of all non-empty non-bss sections, not just those expected to contain instructions. -j may be used to select specific sections. This option also has a subtle effect on the disassembly of instructions in code sections. When option -d is in effect objdump will assume that any symbols present in a code section occur on the boundary between instructions and it will refuse to disassemble across such a boundary. When option -D is in effect however this assumption is supressed. This means that it is possible for the output of -d and -D to differ if, for example, data is stored in code sections. If the target is an ARM architecture this switch also has the effect of forcing the disassembler to decode pieces of data found in code sections as if they were instructions. Note if the --dwarf=follow-links option is enabled then any symbol tables in linked debug info files will be read in and used when disassembling. --no-addresses When disassembling, don't print addresses on each line or for symbols and relocation offsets. In combination with --no-show-raw-insn this may be useful for comparing compiler output. --prefix-addresses When disassembling, print the complete address on each line. This is the older disassembly format. -EB -EL --endian={big|little} Specify the endianness of the object files. This only affects disassembly. This can be useful when disassembling a file format which does not describe endianness information, such as S-records. -f --file-headers Display summary information from the overall header of each of the objfile files. -F --file-offsets When disassembling sections, whenever a symbol is displayed, also display the file offset of the region of data that is about to be dumped. If zeroes are being skipped, then when disassembly resumes, tell the user how many zeroes were skipped and the file offset of the location from where the disassembly resumes. When dumping sections, display the file offset of the location from where the dump starts. --file-start-context Specify that when displaying interlisted source code/disassembly (assumes -S) from a file that has not yet been displayed, extend the context to the start of the file. -h --section-headers --headers Display summary information from the section headers of the object file. File segments may be relocated to nonstandard addresses, for example by using the -Ttext, -Tdata, or -Tbss options to ld. However, some object file formats, such as a.out, do not store the starting address of the file segments. In those situations, although ld relocates the sections correctly, using objdump -h to list the file section headers cannot show the correct addresses. Instead, it shows the usual addresses, which are implicit for the target. Note, in some cases it is possible for a section to have both the READONLY and the NOREAD attributes set. In such cases the NOREAD attribute takes precedence, but objdump will report both since the exact setting of the flag bits might be important. -H --help Print a summary of the options to objdump and exit. -i --info Display a list showing all architectures and object formats available for specification with -b or -m. -j name --section=name Display information for section name. This option may be specified multiple times. -L --process-links Display the contents of non-debug sections found in separate debuginfo files that are linked to the main file. This option automatically implies the -WK option, and only sections requested by other command line options will be displayed. -l --line-numbers Label the display (using debugging information) with the filename and source line numbers corresponding to the object code or relocs shown. Only useful with -d, -D, or -r. -m machine --architecture=machine Specify the architecture to use when disassembling object files. This can be useful when disassembling object files which do not describe architecture information, such as S-records. You can list the available architectures with the -i option. For most architectures it is possible to supply an architecture name and a machine name, separated by a colon. For example foo:bar would refer to the bar machine type in the foo architecture. This can be helpful if objdump has been configured to support multiple architectures. If the target is an ARM architecture then this switch has an additional effect. It restricts the disassembly to only those instructions supported by the architecture specified by machine. If it is necessary to use this switch because the input file does not contain any architecture information, but it is also desired to disassemble all the instructions use -marm. -M options --disassembler-options=options Pass target specific information to the disassembler. Only supported on some targets. If it is necessary to specify more than one disassembler option then multiple -M options can be used or can be placed together into a comma separated list. For ARC, dsp controls the printing of DSP instructions, spfp selects the printing of FPX single precision FP instructions, dpfp selects the printing of FPX double precision FP instructions, quarkse_em selects the printing of special QuarkSE-EM instructions, fpuda selects the printing of double precision assist instructions, fpus selects the printing of FPU single precision FP instructions, while fpud selects the printing of FPU double precision FP instructions. Additionally, one can choose to have all the immediates printed in hexadecimal using hex. By default, the short immediates are printed using the decimal representation, while the long immediate values are printed as hexadecimal. cpu=... allows one to enforce a particular ISA when disassembling instructions, overriding the -m value or whatever is in the ELF file. This might be useful to select ARC EM or HS ISA, because architecture is same for those and disassembler relies on private ELF header data to decide if code is for EM or HS. This option might be specified multiple times - only the latest value will be used. Valid values are same as for the assembler -mcpu=... option. If the target is an ARM architecture then this switch can be used to select which register name set is used during disassembler. Specifying -M reg-names-std (the default) will select the register names as used in ARM's instruction set documentation, but with register 13 called 'sp', register 14 called 'lr' and register 15 called 'pc'. Specifying -M reg-names-apcs will select the name set used by the ARM Procedure Call Standard, whilst specifying -M reg-names-raw will just use r followed by the register number. There are also two variants on the APCS register naming scheme enabled by -M reg- names-atpcs and -M reg-names-special-atpcs which use the ARM/Thumb Procedure Call Standard naming conventions. (Either with the normal register names or the special register names). This option can also be used for ARM architectures to force the disassembler to interpret all instructions as Thumb instructions by using the switch --disassembler-options=force-thumb. This can be useful when attempting to disassemble thumb code produced by other compilers. For AArch64 targets this switch can be used to set whether instructions are disassembled as the most general instruction using the -M no-aliases option or whether instruction notes should be generated as comments in the disasssembly using -M notes. For the x86, some of the options duplicate functions of the -m switch, but allow finer grained control. "x86-64" "i386" "i8086" Select disassembly for the given architecture. "intel" "att" Select between intel syntax mode and AT&T syntax mode. "amd64" "intel64" Select between AMD64 ISA and Intel64 ISA. "intel-mnemonic" "att-mnemonic" Select between intel mnemonic mode and AT&T mnemonic mode. Note: "intel-mnemonic" implies "intel" and "att-mnemonic" implies "att". "addr64" "addr32" "addr16" "data32" "data16" Specify the default address size and operand size. These five options will be overridden if "x86-64", "i386" or "i8086" appear later in the option string. "suffix" When in AT&T mode and also for a limited set of instructions when in Intel mode, instructs the disassembler to print a mnemonic suffix even when the suffix could be inferred by the operands or, for certain instructions, the execution mode's defaults. For PowerPC, the -M argument raw selects disasssembly of hardware insns rather than aliases. For example, you will see "rlwinm" rather than "clrlwi", and "addi" rather than "li". All of the -m arguments for gas that select a CPU are supported. These are: 403, 405, 440, 464, 476, 601, 603, 604, 620, 7400, 7410, 7450, 7455, 750cl, 821, 850, 860, a2, booke, booke32, cell, com, e200z2, e200z4, e300, e500, e500mc, e500mc64, e500x2, e5500, e6500, efs, power4, power5, power6, power7, power8, power9, power10, ppc, ppc32, ppc64, ppc64bridge, ppcps, pwr, pwr2, pwr4, pwr5, pwr5x, pwr6, pwr7, pwr8, pwr9, pwr10, pwrx, titan, vle, and future. 32 and 64 modify the default or a prior CPU selection, disabling and enabling 64-bit insns respectively. In addition, altivec, any, lsp, htm, vsx, spe and spe2 add capabilities to a previous or later CPU selection. any will disassemble any opcode known to binutils, but in cases where an opcode has two different meanings or different arguments, you may not see the disassembly you expect. If you disassemble without giving a CPU selection, a default will be chosen from information gleaned by BFD from the object files headers, but the result again may not be as you expect. For MIPS, this option controls the printing of instruction mnemonic names and register names in disassembled instructions. Multiple selections from the following may be specified as a comma separated string, and invalid options are ignored: "no-aliases" Print the 'raw' instruction mnemonic instead of some pseudo instruction mnemonic. I.e., print 'daddu' or 'or' instead of 'move', 'sll' instead of 'nop', etc. "msa" Disassemble MSA instructions. "virt" Disassemble the virtualization ASE instructions. "xpa" Disassemble the eXtended Physical Address (XPA) ASE instructions. "gpr-names=ABI" Print GPR (general-purpose register) names as appropriate for the specified ABI. By default, GPR names are selected according to the ABI of the binary being disassembled. "fpr-names=ABI" Print FPR (floating-point register) names as appropriate for the specified ABI. By default, FPR numbers are printed rather than names. "cp0-names=ARCH" Print CP0 (system control coprocessor; coprocessor 0) register names as appropriate for the CPU or architecture specified by ARCH. By default, CP0 register names are selected according to the architecture and CPU of the binary being disassembled. "hwr-names=ARCH" Print HWR (hardware register, used by the "rdhwr" instruction) names as appropriate for the CPU or architecture specified by ARCH. By default, HWR names are selected according to the architecture and CPU of the binary being disassembled. "reg-names=ABI" Print GPR and FPR names as appropriate for the selected ABI. "reg-names=ARCH" Print CPU-specific register names (CP0 register and HWR names) as appropriate for the selected CPU or architecture. For any of the options listed above, ABI or ARCH may be specified as numeric to have numbers printed rather than names, for the selected types of registers. You can list the available values of ABI and ARCH using the --help option. For VAX, you can specify function entry addresses with -M entry:0xf00ba. You can use this multiple times to properly disassemble VAX binary files that don't contain symbol tables (like ROM dumps). In these cases, the function entry mask would otherwise be decoded as VAX instructions, which would probably lead the rest of the function being wrongly disassembled. -p --private-headers Print information that is specific to the object file format. The exact information printed depends upon the object file format. For some object file formats, no additional information is printed. -P options --private=options Print information that is specific to the object file format. The argument options is a comma separated list that depends on the format (the lists of options is displayed with the help). For XCOFF, the available options are: "header" "aout" "sections" "syms" "relocs" "lineno," "loader" "except" "typchk" "traceback" "toc" "ldinfo" For PE, the available options are: "header" "sections" Not all object formats support this option. In particular the ELF format does not use it. -r --reloc Print the relocation entries of the file. If used with -d or -D, the relocations are printed interspersed with the disassembly. -R --dynamic-reloc Print the dynamic relocation entries of the file. This is only meaningful for dynamic objects, such as certain types of shared libraries. As for -r, if used with -d or -D, the relocations are printed interspersed with the disassembly. -s --full-contents Display the full contents of sections, often used in combination with -j to request specific sections. By default all non-empty non-bss sections are displayed. By default any compressed section will be displayed in its compressed form. In order to see the contents in a decompressed form add the -Z option to the command line. -S --source Display source code intermixed with disassembly, if possible. Implies -d. --show-all-symbols When disassembling, show all the symbols that match a given address, not just the first one. --source-comment[=txt] Like the -S option, but all source code lines are displayed with a prefix of txt. Typically txt will be a comment string which can be used to distinguish the assembler code from the source code. If txt is not provided then a default string of "# " (hash followed by a space), will be used. --prefix=prefix Specify prefix to add to the absolute paths when used with -S. --prefix-strip=level Indicate how many initial directory names to strip off the hardwired absolute paths. It has no effect without --prefix=prefix. --show-raw-insn When disassembling instructions, print the instruction in hex as well as in symbolic form. This is the default except when --prefix-addresses is used. --no-show-raw-insn When disassembling instructions, do not print the instruction bytes. This is the default when --prefix-addresses is used. --insn-width=width Display width bytes on a single line when disassembling instructions. --visualize-jumps[=color|=extended-color|=off] Visualize jumps that stay inside a function by drawing ASCII art between the start and target addresses. The optional =color argument adds color to the output using simple terminal colors. Alternatively the =extended-color argument will add color using 8bit colors, but these might not work on all terminals. If it is necessary to disable the visualize-jumps option after it has previously been enabled then use visualize-jumps=off. --disassembler-color=off --disassembler-color=terminal --disassembler-color=on|color|colour --disassembler-color=extened|extended-color|extened-colour Enables or disables the use of colored syntax highlighting in disassembly output. The default behaviour is determined via a configure time option. Note, not all architectures support colored syntax highlighting, and depending upon the terminal used, colored output may not actually be legible. The on argument adds colors using simple terminal colors. The terminal argument does the same, but only if the output device is a terminal. The extended-color argument is similar to the on argument, but it uses 8-bit colors. These may not work on all terminals. The off argument disables colored disassembly. -W[lLiaprmfFsoORtUuTgAckK] --dwarf[=rawline,=decodedline,=info,=abbrev,=pubnames,=aranges,=macro,=frames,=frames-interp,=str,=str-offsets,=loc,=Ranges,=pubtypes,=trace_info,=trace_abbrev,=trace_aranges,=gdb_index,=addr,=cu_index,=links,=follow-links] Displays the contents of the DWARF debug sections in the file, if any are present. Compressed debug sections are automatically decompressed (temporarily) before they are displayed. If one or more of the optional letters or words follows the switch then only those type(s) of data will be dumped. The letters and words refer to the following information: "a" "=abbrev" Displays the contents of the .debug_abbrev section. "A" "=addr" Displays the contents of the .debug_addr section. "c" "=cu_index" Displays the contents of the .debug_cu_index and/or .debug_tu_index sections. "f" "=frames" Display the raw contents of a .debug_frame section. "F" "=frames-interp" Display the interpreted contents of a .debug_frame section. "g" "=gdb_index" Displays the contents of the .gdb_index and/or .debug_names sections. "i" "=info" Displays the contents of the .debug_info section. Note: the output from this option can also be restricted by the use of the --dwarf-depth and --dwarf-start options. "k" "=links" Displays the contents of the .gnu_debuglink, .gnu_debugaltlink and .debug_sup sections, if any of them are present. Also displays any links to separate dwarf object files (dwo), if they are specified by the DW_AT_GNU_dwo_name or DW_AT_dwo_name attributes in the .debug_info section. "K" "=follow-links" Display the contents of any selected debug sections that are found in linked, separate debug info file(s). This can result in multiple versions of the same debug section being displayed if it exists in more than one file. In addition, when displaying DWARF attributes, if a form is found that references the separate debug info file, then the referenced contents will also be displayed. Note - in some distributions this option is enabled by default. It can be disabled via the N debug option. The default can be chosen when configuring the binutils via the --enable-follow-debug-links=yes or --enable-follow-debug-links=no options. If these are not used then the default is to enable the following of debug links. Note - if support for the debuginfod protocol was enabled when the binutils were built then this option will also include an attempt to contact any debuginfod servers mentioned in the DEBUGINFOD_URLS environment variable. This could take some time to resolve. This behaviour can be disabled via the =do-not-use-debuginfod debug option. "N" "=no-follow-links" Disables the following of links to separate debug info files. "D" "=use-debuginfod" Enables contacting debuginfod servers if there is a need to follow debug links. This is the default behaviour. "E" "=do-not-use-debuginfod" Disables contacting debuginfod servers when there is a need to follow debug links. "l" "=rawline" Displays the contents of the .debug_line section in a raw format. "L" "=decodedline" Displays the interpreted contents of the .debug_line section. "m" "=macro" Displays the contents of the .debug_macro and/or .debug_macinfo sections. "o" "=loc" Displays the contents of the .debug_loc and/or .debug_loclists sections. "O" "=str-offsets" Displays the contents of the .debug_str_offsets section. "p" "=pubnames" Displays the contents of the .debug_pubnames and/or .debug_gnu_pubnames sections. "r" "=aranges" Displays the contents of the .debug_aranges section. "R" "=Ranges" Displays the contents of the .debug_ranges and/or .debug_rnglists sections. "s" "=str" Displays the contents of the .debug_str, .debug_line_str and/or .debug_str_offsets sections. "t" "=pubtype" Displays the contents of the .debug_pubtypes and/or .debug_gnu_pubtypes sections. "T" "=trace_aranges" Displays the contents of the .trace_aranges section. "u" "=trace_abbrev" Displays the contents of the .trace_abbrev section. "U" "=trace_info" Displays the contents of the .trace_info section. Note: displaying the contents of .debug_static_funcs, .debug_static_vars and debug_weaknames sections is not currently supported. --dwarf-depth=n Limit the dump of the ".debug_info" section to n children. This is only useful with --debug-dump=info. The default is to print all DIEs; the special value 0 for n will also have this effect. With a non-zero value for n, DIEs at or deeper than n levels will not be printed. The range for n is zero-based. --dwarf-start=n Print only DIEs beginning with the DIE numbered n. This is only useful with --debug-dump=info. If specified, this option will suppress printing of any header information and all DIEs before the DIE numbered n. Only siblings and children of the specified DIE will be printed. This can be used in conjunction with --dwarf-depth. --dwarf-check Enable additional checks for consistency of Dwarf information. --ctf[=section] Display the contents of the specified CTF section. CTF sections themselves contain many subsections, all of which are displayed in order. By default, display the name of the section named .ctf, which is the name emitted by ld. --ctf-parent=member If the CTF section contains ambiguously-defined types, it will consist of an archive of many CTF dictionaries, all inheriting from one dictionary containing unambiguous types. This member is by default named .ctf, like the section containing it, but it is possible to change this name using the "ctf_link_set_memb_name_changer" function at link time. When looking at CTF archives that have been created by a linker that uses the name changer to rename the parent archive member, --ctf-parent can be used to specify the name used for the parent. --sframe[=section] Display the contents of the specified SFrame section. By default, display the name of the section named .sframe, which is the name emitted by ld. -G --stabs Display the full contents of any sections requested. Display the contents of the .stab and .stab.index and .stab.excl sections from an ELF file. This is only useful on systems (such as Solaris 2.0) in which ".stab" debugging symbol-table entries are carried in an ELF section. In most other file formats, debugging symbol-table entries are interleaved with linkage symbols, and are visible in the --syms output. --start-address=address Start displaying data at the specified address. This affects the output of the -d, -r and -s options. --stop-address=address Stop displaying data at the specified address. This affects the output of the -d, -r and -s options. -t --syms Print the symbol table entries of the file. This is similar to the information provided by the nm program, although the display format is different. The format of the output depends upon the format of the file being dumped, but there are two main types. One looks like this: [ 4](sec 3)(fl 0x00)(ty 0)(scl 3) (nx 1) 0x00000000 .bss [ 6](sec 1)(fl 0x00)(ty 0)(scl 2) (nx 0) 0x00000000 fred where the number inside the square brackets is the number of the entry in the symbol table, the sec number is the section number, the fl value are the symbol's flag bits, the ty number is the symbol's type, the scl number is the symbol's storage class and the nx value is the number of auxiliary entries associated with the symbol. The last two fields are the symbol's value and its name. The other common output format, usually seen with ELF based files, looks like this: 00000000 l d .bss 00000000 .bss 00000000 g .text 00000000 fred Here the first number is the symbol's value (sometimes referred to as its address). The next field is actually a set of characters and spaces indicating the flag bits that are set on the symbol. These characters are described below. Next is the section with which the symbol is associated or *ABS* if the section is absolute (ie not connected with any section), or *UND* if the section is referenced in the file being dumped, but not defined there. After the section name comes another field, a number, which for common symbols is the alignment and for other symbol is the size. Finally the symbol's name is displayed. The flag characters are divided into 7 groups as follows: "l" "g" "u" "!" The symbol is a local (l), global (g), unique global (u), neither global nor local (a space) or both global and local (!). A symbol can be neither local or global for a variety of reasons, e.g., because it is used for debugging, but it is probably an indication of a bug if it is ever both local and global. Unique global symbols are a GNU extension to the standard set of ELF symbol bindings. For such a symbol the dynamic linker will make sure that in the entire process there is just one symbol with this name and type in use. "w" The symbol is weak (w) or strong (a space). "C" The symbol denotes a constructor (C) or an ordinary symbol (a space). "W" The symbol is a warning (W) or a normal symbol (a space). A warning symbol's name is a message to be displayed if the symbol following the warning symbol is ever referenced. "I" "i" The symbol is an indirect reference to another symbol (I), a function to be evaluated during reloc processing (i) or a normal symbol (a space). "d" "D" The symbol is a debugging symbol (d) or a dynamic symbol (D) or a normal symbol (a space). "F" "f" "O" The symbol is the name of a function (F) or a file (f) or an object (O) or just a normal symbol (a space). -T --dynamic-syms Print the dynamic symbol table entries of the file. This is only meaningful for dynamic objects, such as certain types of shared libraries. This is similar to the information provided by the nm program when given the -D (--dynamic) option. The output format is similar to that produced by the --syms option, except that an extra field is inserted before the symbol's name, giving the version information associated with the symbol. If the version is the default version to be used when resolving unversioned references to the symbol then it's displayed as is, otherwise it's put into parentheses. --special-syms When displaying symbols include those which the target considers to be special in some way and which would not normally be of interest to the user. -U [d|i|l|e|x|h] --unicode=[default|invalid|locale|escape|hex|highlight] Controls the display of UTF-8 encoded multibyte characters in strings. The default (--unicode=default) is to give them no special treatment. The --unicode=locale option displays the sequence in the current locale, which may or may not support them. The options --unicode=hex and --unicode=invalid display them as hex byte sequences enclosed by either angle brackets or curly braces. The --unicode=escape option displays them as escape sequences (\uxxxx) and the --unicode=highlight option displays them as escape sequences highlighted in red (if supported by the output device). The colouring is intended to draw attention to the presence of unicode sequences where they might not be expected. -V --version Print the version number of objdump and exit. -x --all-headers Display all available header information, including the symbol table and relocation entries. Using -x is equivalent to specifying all of -a -f -h -p -r -t. -w --wide Format some lines for output devices that have more than 80 columns. Also do not truncate symbol names when they are displayed. -z --disassemble-zeroes Normally the disassembly output will skip blocks of zeroes. This option directs the disassembler to disassemble those blocks, just like any other data. -Z --decompress The -Z option is meant to be used in conunction with the -s option. It instructs objdump to decompress any compressed sections before displaying their contents. @file Read command-line options from file. The options read are inserted in place of the original @file option. If file does not exist, or cannot be read, then the option will be treated literally, and not removed. Options in file are separated by whitespace. A whitespace character may be included in an option by surrounding the entire option in either single or double quotes. Any character (including a backslash) may be included by prefixing the character to be included with a backslash. The file may itself contain additional @file options; any such options will be processed recursively. SEE ALSO nm(1), readelf(1), and the Info entries for binutils. COPYRIGHT Copyright (c) 1991-2024 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License". binutils-2.42 2023-09-02 OBJDUMP(1)
riscvURLメモ
はじめに RiscVのURLをメモ。 URL https://hazm.at/mox/arch/isa/risc-v/the-risc-v-instruction-set-manual/vol1/index.html
x86メモ
はじめに x86のチートシートURLをメモ。 わかりやすいGithubレポジトリがあったので、フォークしたURLをメモします。 (外部の方のURLだと消える可能性があるので、念のためフォークしています。) URL チートシート https://github.com/tetz-akaneya/x86 システムコールと番号対応表 https://github.com/7etsuo/x86/blob/main/x86-linux-syscalls-cheatsheet.md (fork元: https://github.com/7etsuo/x86)
Asciiテーブルメモ
はじめに ネット検索で毎回違うページを探しているので、自分用にまとめる。 man ascii より引用 ascii(7) Miscellaneous Information Manual ascii(7) NAME ascii - ASCII character set encoded in octal, decimal, and hexadecimal DESCRIPTION ASCII is the American Standard Code for Information Interchange. It is a 7-bit code. Many 8-bit codes (e.g., ISO/IEC 8859-1) contain ASCII as their lower half. The international counterpart of ASCII is known as ISO/IEC 646-IRV. The following table contains the 128 ASCII characters. C program '\X' escapes are noted. Oct Dec Hex Char Oct Dec Hex Char ──────────────────────────────────────────────────────────────────────── 000 0 00 NUL '\0' (null character) 100 64 40 @ 001 1 01 SOH (start of heading) 101 65 41 A 002 2 02 STX (start of text) 102 66 42 B 003 3 03 ETX (end of text) 103 67 43 C 004 4 04 EOT (end of transmission) 104 68 44 D 005 5 05 ENQ (enquiry) 105 69 45 E 006 6 06 ACK (acknowledge) 106 70 46 F 007 7 07 BEL '\a' (bell) 107 71 47 G 010 8 08 BS '\b' (backspace) 110 72 48 H 011 9 09 HT '\t' (horizontal tab) 111 73 49 I 012 10 0A LF '\n' (new line) 112 74 4A J 013 11 0B VT '\v' (vertical tab) 113 75 4B K 014 12 0C FF '\f' (form feed) 114 76 4C L 015 13 0D CR '\r' (carriage ret) 115 77 4D M 016 14 0E SO (shift out) 116 78 4E N 017 15 0F SI (shift in) 117 79 4F O 020 16 10 DLE (data link escape) 120 80 50 P 021 17 11 DC1 (device control 1) 121 81 51 Q 022 18 12 DC2 (device control 2) 122 82 52 R 023 19 13 DC3 (device control 3) 123 83 53 S 024 20 14 DC4 (device control 4) 124 84 54 T 025 21 15 NAK (negative ack.) 125 85 55 U 026 22 16 SYN (synchronous idle) 126 86 56 V 027 23 17 ETB (end of trans. blk) 127 87 57 W 030 24 18 CAN (cancel) 130 88 58 X 031 25 19 EM (end of medium) 131 89 59 Y 032 26 1A SUB (substitute) 132 90 5A Z 033 27 1B ESC (escape) 133 91 5B [ 034 28 1C FS (file separator) 134 92 5C \ '\\' 035 29 1D GS (group separator) 135 93 5D ] 036 30 1E RS (record separator) 136 94 5E ^ 037 31 1F US (unit separator) 137 95 5F _ 040 32 20 SPACE 140 96 60 ` 041 33 21 ! 141 97 61 a 042 34 22 " 142 98 62 b 043 35 23 # 143 99 63 c 044 36 24 $ 144 100 64 d 045 37 25 % 145 101 65 e 046 38 26 & 146 102 66 f 047 39 27 ' 147 103 67 g 050 40 28 ( 150 104 68 h 051 41 29 ) 151 105 69 i 052 42 2A * 152 106 6A j 053 43 2B + 153 107 6B k 054 44 2C , 154 108 6C l 055 45 2D - 155 109 6D m 056 46 2E . 156 110 6E n 057 47 2F / 157 111 6F o 060 48 30 0 160 112 70 p 061 49 31 1 161 113 71 q 062 50 32 2 162 114 72 r 063 51 33 3 163 115 73 s 064 52 34 4 164 116 74 t 065 53 35 5 165 117 75 u 066 54 36 6 166 118 76 v 067 55 37 7 167 119 77 w 070 56 38 8 170 120 78 x 071 57 39 9 171 121 79 y 072 58 3A : 172 122 7A z 073 59 3B ; 173 123 7B { 074 60 3C < 174 124 7C | 075 61 3D = 175 125 7D } 076 62 3E > 176 126 7E ~ 077 63 3F ? │ 177 127 7F DEL │ Tables │ For convenience, below are more compact tables in hex and decimal. 2 3 4 5 6 7 30 40 50 60 70 80 90 100 110 120 ------------- --------------------------------- 0: 0 @ P ` p 0: ( 2 < F P Z d n x 1: ! 1 A Q a q 1: ) 3 = G Q [ e o y 2: " 2 B R b r 2: * 4 > H R \ f p z 3: # 3 C S c s 3: ! + 5 ? I S ] g q { 4: $ 4 D T d t 4: " , 6 @ J T ^ h r | 5: % 5 E U e u 5: # - 7 A K U _ i s } 6: & 6 F V f v 6: $ . 8 B L V ` j t ~ 7: ' 7 G W g w 7: % / 9 C M W a k u DEL 8: ( 8 H X h x 8: & 0 : D N X b l v 9: ) 9 I Y i y 9: ' 1 ; E O Y c m w A: * : J Z j z B: + ; K [ k { C: , < L \ l | D: - = M ] m } E: . > N ^ n ~ F: / ? O _ o DEL NOTES History /etc/ascii (VII) appears in the UNIX Programmer's Manual. On older terminals, the underscore code is displayed as a left arrow, called backarrow, the caret is displayed as an up-arrow and the verti‐ cal bar has a hole in the middle. Uppercase and lowercase characters differ by just one bit and the ASCII character 2 differs from the double quote by just one bit, too. That made it much easier to encode characters mechanically or with a non-mi‐ crocontroller-based electronic keyboard and that pairing was found on old teletypes. The ASCII standard was published by the United States of America Stan‐ dards Institute (USASI) in 1968. SEE ALSO charsets(7), iso_8859-1(7), iso_8859-2(7), iso_8859-3(7), iso_8859-4(7), iso_8859-5(7), iso_8859-6(7), iso_8859-7(7), iso_8859-8(7), iso_8859-9(7), iso_8859-10(7), iso_8859-11(7), iso_8859-13(7), iso_8859-14(7), iso_8859-15(7), iso_8859-16(7), utf-8(7) Linux man-pages 6.7 2024-01-28 ascii(7)
aptコマンドメモ
はじめに よく忘れるのでメモ man aptより引用 APT(8) APT APT(8) NAME apt - command-line interface SYNOPSIS apt [-h] [-o=config_string] [-c=config_file] [-t=target_release] [-a=architecture] {list | search | show | update | install pkg [{=pkg_version_number | /target_release}]... | remove pkg... | upgrade | full-upgrade | edit-sources | {-v | --version} | {-h | --help}} DESCRIPTION apt provides a high-level commandline interface for the package management system. It is intended as an end user interface and enables some options better suited for interactive usage by default compared to more specialized APT tools like apt-get(8) and apt- cache(8). Much like apt itself, its manpage is intended as an end user interface and as such only mentions the most used commands and options partly to not duplicate information in multiple places and partly to avoid overwhelming readers with a cornucopia of options and details. update (apt-get(8)) update is used to download package information from all configured sources. Other commands operate on this data to e.g. perform package upgrades or search in and display details about all packages available for installation. upgrade (apt-get(8)) upgrade is used to install available upgrades of all packages currently installed on the system from the sources configured via sources.list(5). New packages will be installed if required to satisfy dependencies, but existing packages will never be removed. If an upgrade for a package requires the removal of an installed package the upgrade for this package isn't performed. When a package is supplied as an argument, the package will be installed prior to the upgrade action. full-upgrade (apt-get(8)) full-upgrade performs the function of upgrade but will remove currently installed packages if this is needed to upgrade the system as a whole. When a package is supplied as an argument, the package will be installed prior to the upgrade action. install, reinstall, remove, purge (apt-get(8)) Performs the requested action on one or more packages specified via regex(7), glob(7) or exact match. The requested action can be overridden for specific packages by appending a plus (+) to the package name to install this package or a minus (-) to remove it. A specific version of a package can be selected for installation by following the package name with an equals (=) and the version of the package to select. Alternatively the version from a specific release can be selected by following the package name with a forward slash (/) and codename (bookworm, trixie, sid ...) or suite name (stable, testing, unstable). This will also select versions from this release for dependencies of this package if needed to satisfy the request. Removing a package removes all packaged data, but leaves usually small (modified) user configuration files behind, in case the remove was an accident. Just issuing an installation request for the accidentally removed package will restore its function as before in that case. On the other hand you can get rid of these leftovers by calling purge even on already removed packages. Note that this does not affect any data or configuration stored in your home directory. autoremove (apt-get(8)) autoremove is used to remove packages that were automatically installed to satisfy dependencies for other packages and are now no longer needed as dependencies changed or the package(s) needing them were removed in the meantime. You should check that the list does not include applications you have grown to like even though they were once installed just as a dependency of another package. You can mark such a package as manually installed by using apt-mark(8). Packages which you have installed explicitly via install are also never proposed for automatic removal. satisfy (apt-get(8)) satisfy satisfies dependency strings, as used in Build-Depends. It also handles conflicts, by prefixing an argument with "Conflicts: ". Example: apt satisfy "foo, bar (>= 1.0)" "Conflicts: baz, fuzz" search (apt-cache(8)) search can be used to search for the given regex(7) term(s) in the list of available packages and display matches. This can e.g. be useful if you are looking for packages having a specific feature. If you are looking for a package including a specific file try apt-file(1). show (apt-cache(8)) Show information about the given package(s) including its dependencies, installation and download size, sources the package is available from, the description of the packages content and much more. It can e.g. be helpful to look at this information before allowing apt(8) to remove a package or while searching for new packages to install. list list is somewhat similar to dpkg-query --list in that it can display a list of packages satisfying certain criteria. It supports glob(7) patterns for matching package names, apt-patterns(7), as well as options to list installed (--installed), upgradeable (--upgradeable) or all available (--all-versions) versions. edit-sources (work-in-progress) edit-sources lets you edit your sources.list(5) files in your preferred text editor while also providing basic sanity checks. showsrc, depends, rdepends, policy (summarised in apt-cache(8)) source, build-dep, download, changelog, clean, distclean, autoclean (summarised in apt- get(8)) SCRIPT USAGE AND DIFFERENCES FROM OTHER APT TOOLS The apt(8) commandline is designed as an end-user tool and it may change behavior between versions. While it tries not to break backward compatibility this is not guaranteed either if a change seems beneficial for interactive use. All features of apt(8) are available in dedicated APT tools like apt-get(8) and apt- cache(8) as well. apt(8) just changes the default value of some options (see apt.conf(5) and specifically the Binary scope). So you should prefer using these commands (potentially with some additional options enabled) in your scripts as they keep backward compatibility as much as possible. SEE ALSO apt-get(8), apt-cache(8), sources.list(5), apt.conf(5), apt-config(8), apt-patterns(7), The APT User's guide in /usr/share/doc/apt-doc/, apt_preferences(5), the APT Howto. DIAGNOSTICS apt returns zero on normal operation, decimal 100 on error. BUGS APT bug page[1]. If you wish to report a bug in APT, please see /usr/share/doc/debian/bug-reporting.txt or the reportbug(1) command. AUTHOR APT team NOTES 1. APT bug page https://bugs.debian.org/src:apt APT 2.7.14 12 March 2024 APT(8)
nftコマンドメモ
はじめに nftコマンドについてメモ。 man nftより引用 NFT(8) NFT(8) NAME nft - Administration tool of the nftables framework for packet filtering and classification SYNOPSIS nft [ -nNscaeSupyjtT ] [ -I directory ] [ -f filename | -i | cmd ...] nft -h nft -v DESCRIPTION nft is the command line tool used to set up, maintain and inspect packet filtering and classification rules in the Linux kernel, in the nftables framework. The Linux kernel subsystem is known as nf_tables, and ‘nf’ stands for Netfilter. OPTIONS The command accepts several different options which are documented here in groups for better understanding of their meaning. You can get information about options by running nft --help. General options: -h, --help Show help message and all options. -v, --version Show version. -V Show long version information, including compile-time configuration. Ruleset input handling options that specify to how to load rulesets: -f, --file filename Read input from filename. If filename is -, read from stdin. -D, --define name=value Define a variable. You can only combine this option with -f. -i, --interactive Read input from an interactive readline CLI. You can use quit to exit, or use the EOF marker, normally this is CTRL-D. -I, --includepath directory Add the directory directory to the list of directories to be searched for included files. This option may be specified multiple times. -c, --check Check commands validity without actually applying the changes. -o, --optimize Optimize your ruleset. You can combine this option with -c to inspect the proposed optimizations. Ruleset list output formatting that modify the output of the list ruleset command: -a, --handle Show object handles in output. -s, --stateless Omit stateful information of rules and stateful objects. -t, --terse Omit contents of sets from output. -S, --service Translate ports to service names as defined by /etc/services. -N, --reversedns Translate IP address to names via reverse DNS lookup. This may slow down your listing since it generates network traffic. -u, --guid Translate numeric UID/GID to names as defined by /etc/passwd and /etc/group. -n, --numeric Print fully numerical output. -y, --numeric-priority Display base chain priority numerically. -p, --numeric-protocol Display layer 4 protocol numerically. -T, --numeric-time Show time, day and hour values in numeric format. Command output formatting: -e, --echo When inserting items into the ruleset using add, insert or replace commands, print notifications just like nft monitor. -j, --json Format output in JSON. See libnftables-json(5) for a schema description. -d, --debug level Enable debugging output. The debug level can be any of scanner, parser, eval, netlink, mnl, proto-ctx, segtree, all. You can combine more than one by separating by the , symbol, for example -d eval,mnl. INPUT FILE FORMATS LEXICAL CONVENTIONS Input is parsed line-wise. When the last character of a line, just before the newline character, is a non-quoted backslash (\), the next line is treated as a continuation. Multiple commands on the same line can be separated using a semicolon (;). A hash sign (#) begins a comment. All following characters on the same line are ignored. Identifiers begin with an alphabetic character (a-z,A-Z), followed by zero or more alphanumeric characters (a-z,A-Z,0-9) and the characters slash (/), backslash (\), underscore (_) and dot (.). Identifiers using different characters or clashing with a keyword need to be enclosed in double quotes ("). INCLUDE FILES include filename Other files can be included by using the include statement. The directories to be searched for include files can be specified using the -I/--includepath option. You can override this behaviour either by prepending ‘./’ to your path to force inclusion of files located in the current working directory (i.e. relative path) or / for file location expressed as an absolute path. If -I/--includepath is not specified, then nft relies on the default directory that is specified at compile time. You can retrieve this default directory via the -h/--help option. Include statements support the usual shell wildcard symbols (,?,[]). Having no matches for an include statement is not an error, if wildcard symbols are used in the include statement. This allows having potentially empty include directories for statements like include "/etc/firewall/rules/". The wildcard matches are loaded in alphabetical order. Files beginning with dot (.) are not matched by include statements. SYMBOLIC VARIABLES define variable = expr undefine variable redefine variable = expr $variable Symbolic variables can be defined using the define statement. Variable references are expressions and can be used to initialize other variables. The scope of a definition is the current block and all blocks contained within. Symbolic variables can be undefined using the undefine statement, and modified using the redefine statement. Using symbolic variables. define int_if1 = eth0 define int_if2 = eth1 define int_ifs = { $int_if1, $int_if2 } redefine int_if2 = wlan0 undefine int_if2 filter input iif $int_ifs accept ADDRESS FAMILIES Address families determine the type of packets which are processed. For each address family, the kernel contains so called hooks at specific stages of the packet processing paths, which invoke nftables if rules for these hooks exist. ip IPv4 address family. ip6 IPv6 address family. inet Internet (IPv4/IPv6) address family. arp ARP address family, handling IPv4 ARP packets. bridge Bridge address family, handling packets which traverse a bridge device. netdev Netdev address family, handling packets on ingress and egress. All nftables objects exist in address family specific namespaces, therefore all identifiers include an address family. If an identifier is specified without an address family, the ip family is used by default. IPV4/IPV6/INET ADDRESS FAMILIES The IPv4/IPv6/Inet address families handle IPv4, IPv6 or both types of packets. They contain five hooks at different packet processing stages in the network stack. Table 1. IPv4/IPv6/Inet address family hooks ┌─────────────┬──────────────────────────────────┐ │ Hook │ Description │ ├─────────────┼──────────────────────────────────┤ │ │ │ │ prerouting │ All packets entering the system │ │ │ are processed by the prerouting │ │ │ hook. It is invoked before the │ │ │ routing process and is used for │ │ │ early filtering or changing │ │ │ packet attributes that affect │ │ │ routing. │ ├─────────────┼──────────────────────────────────┤ │ │ │ │ input │ Packets delivered to the local │ │ │ system are processed by the │ │ │ input hook. │ ├─────────────┼──────────────────────────────────┤ │ │ │ │ forward │ Packets forwarded to a different │ │ │ host are processed by the │ │ │ forward hook. │ ├─────────────┼──────────────────────────────────┤ │ │ │ │ output │ Packets sent by local processes │ │ │ are processed by the output │ │ │ hook. │ ├─────────────┼──────────────────────────────────┤ │ │ │ │ postrouting │ All packets leaving the system │ │ │ are processed by the postrouting │ │ │ hook. │ ├─────────────┼──────────────────────────────────┤ │ │ │ │ ingress │ All packets entering the system │ │ │ are processed by this hook. It │ │ │ is invoked before layer 3 │ │ │ protocol handlers, hence before │ │ │ the prerouting hook, and it can │ │ │ be used for filtering and │ │ │ policing. Ingress is only │ │ │ available for Inet family (since │ │ │ Linux kernel 5.10). │ └─────────────┴──────────────────────────────────┘ ARP ADDRESS FAMILY The ARP address family handles ARP packets received and sent by the system. It is commonly used to mangle ARP packets for clustering. Table 2. ARP address family hooks ┌────────┬──────────────────────────────────┐ │ Hook │ Description │ ├────────┼──────────────────────────────────┤ │ │ │ │ input │ Packets delivered to the local │ │ │ system are processed by the │ │ │ input hook. │ ├────────┼──────────────────────────────────┤ │ │ │ │ output │ Packets send by the local system │ │ │ are processed by the output │ │ │ hook. │ └────────┴──────────────────────────────────┘ BRIDGE ADDRESS FAMILY The bridge address family handles Ethernet packets traversing bridge devices. The list of supported hooks is identical to IPv4/IPv6/Inet address families above. NETDEV ADDRESS FAMILY The Netdev address family handles packets from the device ingress and egress path. This family allows you to filter packets of any ethertype such as ARP, VLAN 802.1q, VLAN 802.1ad (Q-in-Q) as well as IPv4 and IPv6 packets. Table 3. Netdev address family hooks ┌─────────┬─────────────────────────────────┐ │ Hook │ Description │ ├─────────┼─────────────────────────────────┤ │ │ │ │ ingress │ All packets entering the system │ │ │ are processed by this hook. It │ │ │ is invoked after the network │ │ │ taps (ie. tcpdump), right after │ │ │ tc ingress and before layer 3 │ │ │ protocol handlers, it can be │ │ │ used for early filtering and │ │ │ policing. │ ├─────────┼─────────────────────────────────┤ │ │ │ │ egress │ All packets leaving the system │ │ │ are processed by this hook. It │ │ │ is invoked after layer 3 │ │ │ protocol handlers and before tc │ │ │ egress. It can be used for late │ │ │ filtering and policing. │ └─────────┴─────────────────────────────────┘ Tunneled packets (such as vxlan) are processed by netdev family hooks both in decapsulated and encapsulated (tunneled) form. So a packet can be filtered on the overlay network as well as on the underlying network. Note that the order of netfilter and tc is mirrored on ingress versus egress. This ensures symmetry for NAT and other packet mangling. Ingress packets which are redirected out some other interface are only processed by netfilter on egress if they have passed through netfilter ingress processing before. Thus, ingress packets which are redirected by tc are not subjected to netfilter. But they are if they are redirected by netfilter on ingress. Conceptually, tc and netfilter can be thought of as layers, with netfilter layered above tc: If the packet hasn’t been passed up from the tc layer to the netfilter layer, it’s not subjected to netfilter on egress. RULESET {list | flush} ruleset [family] The ruleset keyword is used to identify the whole set of tables, chains, etc. currently in place in kernel. The following ruleset commands exist: list Print the ruleset in human-readable format. flush Clear the whole ruleset. Note that, unlike iptables, this will remove all tables and whatever they contain, effectively leading to an empty ruleset - no packet filtering will happen anymore, so the kernel accepts any valid packet it receives. It is possible to limit list and flush to a specific address family only. For a list of valid family names, see the section called “ADDRESS FAMILIES” above. By design, list ruleset command output may be used as input to nft -f. Effectively, this is the nft-equivalent of iptables-save and iptables-restore. TABLES {add | create} table [family] table [ {comment comment ;} { flags 'flags ; }] {delete | destroy | list | flush} table [family] table list tables [family] delete table [family] handle handle destroy table [family] handle handle Tables are containers for chains, sets and stateful objects. They are identified by their address family and their name. The address family must be one of ip, ip6, inet, arp, bridge, netdev. The inet address family is a dummy family which is used to create hybrid IPv4/IPv6 tables. The meta expression nfproto keyword can be used to test which family (ipv4 or ipv6) context the packet is being processed in. When no address family is specified, ip is used by default. The only difference between add and create is that the former will not return an error if the specified table already exists while create will return an error. Table 4. Table flags ┌─────────┬─────────────────────────────────┐ │ Flag │ Description │ ├─────────┼─────────────────────────────────┤ │ │ │ │ dormant │ table is not evaluated any more │ │ │ (base chains are unregistered). │ └─────────┴─────────────────────────────────┘ Add, change, delete a table. # start nft in interactive mode nft --interactive # create a new table. create table inet mytable # add a new base chain: get input packets add chain inet mytable myin { type filter hook input priority filter; } # add a single counter to the chain add rule inet mytable myin counter # disable the table temporarily -- rules are not evaluated anymore add table inet mytable { flags dormant; } # make table active again: add table inet mytable add Add a new table for the given family with the given name. delete Delete the specified table. destroy Delete the specified table, it does not fail if it does not exist. list List all chains and rules of the specified table. flush Flush all chains and rules of the specified table. CHAINS {add | create} chain [family] table chain [{ type type hook hook [device device] priority priority ; [policy policy ;] [comment comment ;] }] {delete | destroy | list | flush} chain ['family] table chain list chains [family] delete chain [family] table handle handle destroy chain [family] table handle handle rename chain [family] table chain newname Chains are containers for rules. They exist in two kinds, base chains and regular chains. A base chain is an entry point for packets from the networking stack, a regular chain may be used as jump target and is used for better rule organization. add Add a new chain in the specified table. When a hook and priority value are specified, the chain is created as a base chain and hooked up to the networking stack. create Similar to the add command, but returns an error if the chain already exists. delete Delete the specified chain. The chain must not contain any rules or be used as jump target. destroy Delete the specified chain, it does not fail if it does not exist. The chain must not contain any rules or be used as jump target. rename Rename the specified chain. list List all rules of the specified chain. flush Flush all rules of the specified chain. For base chains, type, hook and priority parameters are mandatory. Table 5. Supported chain types ┌────────┬───────────────┬─────────────────────┬─────────────────────┐ │ Type │ Families │ Hooks │ Description │ ├────────┼───────────────┼─────────────────────┼─────────────────────┤ │ │ │ │ │ │ filter │ all │ all │ Standard chain type │ │ │ │ │ to use in doubt. │ ├────────┼───────────────┼─────────────────────┼─────────────────────┤ │ │ │ │ │ │ nat │ ip, ip6, inet │ prerouting, input, │ Chains of this type │ │ │ │ output, postrouting │ perform Native │ │ │ │ │ Address Translation │ │ │ │ │ based on conntrack │ │ │ │ │ entries. Only the │ │ │ │ │ first packet of a │ │ │ │ │ connection actually │ │ │ │ │ traverses this │ │ │ │ │ chain - its rules │ │ │ │ │ usually define │ │ │ │ │ details of the │ │ │ │ │ created conntrack │ │ │ │ │ entry (NAT │ │ │ │ │ statements for │ │ │ │ │ instance). │ ├────────┼───────────────┼─────────────────────┼─────────────────────┤ │ │ │ │ │ │ route │ ip, ip6 │ output │ If a packet has │ │ │ │ │ traversed a chain │ │ │ │ │ of this type and is │ │ │ │ │ about to be │ │ │ │ │ accepted, a new │ │ │ │ │ route lookup is │ │ │ │ │ performed if │ │ │ │ │ relevant parts of │ │ │ │ │ the IP header have │ │ │ │ │ changed. This │ │ │ │ │ allows one to e.g. │ │ │ │ │ implement policy │ │ │ │ │ routing selectors │ │ │ │ │ in nftables. │ └────────┴───────────────┴─────────────────────┴─────────────────────┘ Apart from the special cases illustrated above (e.g. nat type not supporting forward hook or route type only supporting output hook), there are three further quirks worth noticing: • The netdev family supports merely two combinations, namely filter type with ingress hook and filter type with egress hook. Base chains in this family also require the device parameter to be present since they exist per interface only. • The arp family supports only the input and output hooks, both in chains of type filter. • The inet family also supports the ingress hook (since Linux kernel 5.10), to filter IPv4 and IPv6 packet at the same location as the netdev ingress hook. This inet hook allows you to share sets and maps between the usual prerouting, input, forward, output, postrouting and this ingress hook. The device parameter accepts a network interface name as a string, and is required when adding a base chain that filters traffic on the ingress or egress hooks. Any ingress or egress chains will only filter traffic from the interface specified in the device parameter. The priority parameter accepts a signed integer value or a standard priority name which specifies the order in which chains with the same hook value are traversed. The ordering is ascending, i.e. lower priority values have precedence over higher ones. With nat type chains, there’s a lower excluding limit of -200 for priority values, because conntrack hooks at this priority and NAT requires it. Standard priority values can be replaced with easily memorizable names. Not all names make sense in every family with every hook (see the compatibility matrices below) but their numerical value can still be used for prioritizing chains. These names and values are defined and made available based on what priorities are used by xtables when registering their default chains. Most of the families use the same values, but bridge uses different ones from the others. See the following tables that describe the values and compatibility. Table 6. Standard priority names, family and hook compatibility matrix ┌──────────┬───────┬─────────────────────┬─────────────┐ │ Name │ Value │ Families │ Hooks │ ├──────────┼───────┼─────────────────────┼─────────────┤ │ │ │ │ │ │ raw │ -300 │ ip, ip6, inet │ all │ ├──────────┼───────┼─────────────────────┼─────────────┤ │ │ │ │ │ │ mangle │ -150 │ ip, ip6, inet │ all │ ├──────────┼───────┼─────────────────────┼─────────────┤ │ │ │ │ │ │ dstnat │ -100 │ ip, ip6, inet │ prerouting │ ├──────────┼───────┼─────────────────────┼─────────────┤ │ │ │ │ │ │ filter │ 0 │ ip, ip6, inet, arp, │ all │ │ │ │ netdev │ │ ├──────────┼───────┼─────────────────────┼─────────────┤ │ │ │ │ │ │ security │ 50 │ ip, ip6, inet │ all │ ├──────────┼───────┼─────────────────────┼─────────────┤ │ │ │ │ │ │ srcnat │ 100 │ ip, ip6, inet │ postrouting │ └──────────┴───────┴─────────────────────┴─────────────┘ Table 7. Standard priority names and hook compatibility for the bridge family ┌────────┬───────┬─────────────┐ │ │ │ │ │ Name │ Value │ Hooks │ ├────────┼───────┼─────────────┤ │ │ │ │ │ dstnat │ -300 │ prerouting │ ├────────┼───────┼─────────────┤ │ │ │ │ │ filter │ -200 │ all │ ├────────┼───────┼─────────────┤ │ │ │ │ │ out │ 100 │ output │ ├────────┼───────┼─────────────┤ │ │ │ │ │ srcnat │ 300 │ postrouting │ └────────┴───────┴─────────────┘ Basic arithmetic expressions (addition and subtraction) can also be achieved with these standard names to ease relative prioritizing, e.g. mangle - 5 stands for -155. Values will also be printed like this until the value is not further than 10 from the standard value. Base chains also allow one to set the chain’s policy, i.e. what happens to packets not explicitly accepted or refused in contained rules. Supported policy values are accept (which is the default) or drop. RULES {add | insert} rule [family] table chain [handle handle | index index] statement ... [comment comment] replace rule [family] table chain handle handle statement ... [comment comment] {delete | reset} rule [family] table chain handle handle destroy rule [family] table chain handle handle reset rules [family] [table [chain]] Rules are added to chains in the given table. If the family is not specified, the ip family is used. Rules are constructed from two kinds of components according to a set of grammatical rules: expressions and statements. The add and insert commands support an optional location specifier, which is either a handle or the index (starting at zero) of an existing rule. Internally, rule locations are always identified by handle and the translation from index happens in userspace. This has two potential implications in case a concurrent ruleset change happens after the translation was done: The effective rule index might change if a rule was inserted or deleted before the referred one. If the referred rule was deleted, the command is rejected by the kernel just as if an invalid handle was given. A comment is a single word or a double-quoted (") multi-word string which can be used to make notes regarding the actual rule. Note: If you use bash for adding rules, you have to escape the quotation marks, e.g. \"enable ssh for servers\". add Add a new rule described by the list of statements. The rule is appended to the given chain unless a location is specified, in which case the rule is inserted after the specified rule. insert Same as add except the rule is inserted at the beginning of the chain or before the specified rule. replace Similar to add, but the rule replaces the specified rule. delete Delete the specified rule. destroy Delete the specified rule, it does not fail if it does not exist. reset Reset rule-contained state, e.g. counter and quota statement values. add a rule to ip table output chain. nft add rule filter output ip daddr 192.168.0.0/24 accept # 'ip filter' is assumed # same command, slightly more verbose nft add rule ip filter output ip daddr 192.168.0.0/24 accept delete rule from inet table. # nft -a list ruleset table inet filter { chain input { type filter hook input priority filter; policy accept; ct state established,related accept # handle 4 ip saddr 10.1.1.1 tcp dport ssh accept # handle 5 ... # delete the rule with handle 5 nft delete rule inet filter input handle 5 SETS nftables offers two kinds of set concepts. Anonymous sets are sets that have no specific name. The set members are enclosed in curly braces, with commas to separate elements when creating the rule the set is used in. Once that rule is removed, the set is removed as well. They cannot be updated, i.e. once an anonymous set is declared it cannot be changed anymore except by removing/altering the rule that uses the anonymous set. Using anonymous sets to accept particular subnets and ports. nft add rule filter input ip saddr { 10.0.0.0/8, 192.168.0.0/16 } tcp dport { 22, 443 } accept Named sets are sets that need to be defined first before they can be referenced in rules. Unlike anonymous sets, elements can be added to or removed from a named set at any time. Sets are referenced from rules using an @ prefixed to the sets name. Using named sets to accept addresses and ports. nft add rule filter input ip saddr @allowed_hosts tcp dport @allowed_ports accept The sets allowed_hosts and allowed_ports need to be created first. The next section describes nft set syntax in more detail. add set [family] table set { type type | typeof expression ; [flags flags ;] [timeout timeout ;] [gc-interval gc-interval ;] [elements = { element[, ...] } ;] [size size ;] [comment comment ;] [policy 'policy ;] [auto-merge ;] } {delete | destroy | list | flush | reset } set [family] table set list sets [family] delete set [family] table handle handle {add | delete | destroy } element [family] table set { element[, ...] } Sets are element containers of a user-defined data type, they are uniquely identified by a user-defined name and attached to tables. Their behaviour can be tuned with the flags that can be specified at set creation time. add Add a new set in the specified table. See the Set specification table below for more information about how to specify properties of a set. delete Delete the specified set. destroy Delete the specified set, it does not fail if it does not exist. list Display the elements in the specified set. flush Remove all elements from the specified set. reset Reset state in all contained elements, e.g. counter and quota statement values. Table 8. Set specifications ┌─────────────┬──────────────────────────┬──────────────────────────┐ │ Keyword │ Description │ Type │ ├─────────────┼──────────────────────────┼──────────────────────────┤ │ │ │ │ │ type │ data type of set │ string: ipv4_addr, │ │ │ elements │ ipv6_addr, ether_addr, │ │ │ │ inet_proto, │ │ │ │ inet_service, mark │ ├─────────────┼──────────────────────────┼──────────────────────────┤ │ │ │ │ │ typeof │ data type of set element │ expression to derive the │ │ │ │ data type from │ ├─────────────┼──────────────────────────┼──────────────────────────┤ │ │ │ │ │ flags │ set flags │ string: constant, │ │ │ │ dynamic, interval, │ │ │ │ timeout. Used to │ │ │ │ describe the sets │ │ │ │ properties. │ ├─────────────┼──────────────────────────┼──────────────────────────┤ │ │ │ │ │ timeout │ time an element stays in │ string, decimal followed │ │ │ the set, mandatory if │ by unit. Units are: d, │ │ │ set is added to from the │ h, m, s │ │ │ packet path (ruleset) │ │ ├─────────────┼──────────────────────────┼──────────────────────────┤ │ │ │ │ │ gc-interval │ garbage collection │ string, decimal followed │ │ │ interval, only available │ by unit. Units are: d, │ │ │ when timeout or flag │ h, m, s │ │ │ timeout are active │ │ ├─────────────┼──────────────────────────┼──────────────────────────┤ │ │ │ │ │ elements │ elements contained by │ set data type │ │ │ the set │ │ ├─────────────┼──────────────────────────┼──────────────────────────┤ │ │ │ │ │ size │ maximum number of │ unsigned integer (64 │ │ │ elements in the set, │ bit) │ │ │ mandatory if set is │ │ │ │ added to from the packet │ │ │ │ path (ruleset) │ │ ├─────────────┼──────────────────────────┼──────────────────────────┤ │ │ │ │ │ policy │ set policy │ string: performance │ │ │ │ [default], memory │ ├─────────────┼──────────────────────────┼──────────────────────────┤ │ │ │ │ │ auto-merge │ automatic merge of │ │ │ │ adjacent/overlapping set │ │ │ │ elements (only for │ │ │ │ interval sets) │ │ └─────────────┴──────────────────────────┴──────────────────────────┘ MAPS add map [family] table map { type type | typeof expression [flags flags ;] [elements = { element[, ...] } ;] [size size ;] [comment comment ;] [policy 'policy ;] } {delete | destroy | list | flush | reset } map [family] table map list maps [family] Maps store data based on some specific key used as input. They are uniquely identified by a user-defined name and attached to tables. add Add a new map in the specified table. delete Delete the specified map. destroy Delete the specified map, it does not fail if it does not exist. list Display the elements in the specified map. flush Remove all elements from the specified map. reset Reset state in all contained elements, e.g. counter and quota statement values. Table 9. Map specifications ┌──────────┬──────────────────────────┬──────────────────────────┐ │ Keyword │ Description │ Type │ ├──────────┼──────────────────────────┼──────────────────────────┤ │ │ │ │ │ type │ data type of map │ string: ipv4_addr, │ │ │ elements │ ipv6_addr, ether_addr, │ │ │ │ inet_proto, │ │ │ │ inet_service, mark, │ │ │ │ counter, quota. Counter │ │ │ │ and quota can’t be used │ │ │ │ as keys │ ├──────────┼──────────────────────────┼──────────────────────────┤ │ │ │ │ │ typeof │ data type of set element │ expression to derive the │ │ │ │ data type from │ ├──────────┼──────────────────────────┼──────────────────────────┤ │ │ │ │ │ flags │ map flags │ string, same as set │ │ │ │ flags │ ├──────────┼──────────────────────────┼──────────────────────────┤ │ │ │ │ │ elements │ elements contained by │ map data type │ │ │ the map │ │ ├──────────┼──────────────────────────┼──────────────────────────┤ │ │ │ │ │ size │ maximum number of │ unsigned integer (64 │ │ │ elements in the map │ bit) │ ├──────────┼──────────────────────────┼──────────────────────────┤ │ │ │ │ │ policy │ map policy │ string: performance │ │ │ │ [default], memory │ └──────────┴──────────────────────────┴──────────────────────────┘ Users can specifiy the properties/features that the set/map must support. This allows the kernel to pick an optimal internal representation. If a required flag is missing, the ruleset might still work, as nftables will auto-enable features if it can infer this from the ruleset. This may not work for all cases, however, so it is recommended to specify all required features in the set/map definition manually. Table 10. Set and Map flags ┌──────────┬────────────────────────────────┐ │ Flag │ Description │ ├──────────┼────────────────────────────────┤ │ │ │ │ constant │ Set contents will never change │ │ │ after creation │ ├──────────┼────────────────────────────────┤ │ │ │ │ dynamic │ Set must support updates from │ │ │ the packet path with the add, │ │ │ update or delete keywords. │ ├──────────┼────────────────────────────────┤ │ │ │ │ interval │ Set must be able to store │ │ │ intervals (ranges) │ ├──────────┼────────────────────────────────┤ │ │ │ │ timeout │ Set must support element │ │ │ timeouts (auto-removal of │ │ │ elements once they expire). │ └──────────┴────────────────────────────────┘ ELEMENTS {add | create | delete | destroy | get | reset } element [family] table set { ELEMENT[, ...] } ELEMENT := key_expression OPTIONS [: value_expression] OPTIONS := [timeout TIMESPEC] [expires TIMESPEC] [comment string] TIMESPEC := [numd][numh][numm][num[s]] Element-related commands allow one to change contents of named sets and maps. key_expression is typically a value matching the set type. value_expression is not allowed in sets but mandatory when adding to maps, where it matches the data part in its type definition. When deleting from maps, it may be specified but is optional as key_expression uniquely identifies the element. create command is similar to add with the exception that none of the listed elements may already exist. get command is useful to check if an element is contained in a set which may be non-trivial in very large and/or interval sets. In the latter case, the containing interval is returned instead of just the element itself. reset command resets state attached to the given element(s), e.g. counter and quota statement values. Table 11. Element options ┌─────────┬──────────────────────────────────┐ │ Option │ Description │ ├─────────┼──────────────────────────────────┤ │ │ │ │ timeout │ timeout value for sets/maps with │ │ │ flag timeout │ ├─────────┼──────────────────────────────────┤ │ │ │ │ expires │ the time until given element │ │ │ expires, useful for ruleset │ │ │ replication only │ ├─────────┼──────────────────────────────────┤ │ │ │ │ comment │ per element comment field │ └─────────┴──────────────────────────────────┘ FLOWTABLES {add | create} flowtable [family] table flowtable { hook hook priority priority ; devices = { device[, ...] } ; } list flowtables [family] {delete | destroy | list} flowtable [family] table flowtable delete flowtable [family] table handle handle Flowtables allow you to accelerate packet forwarding in software. Flowtables entries are represented through a tuple that is composed of the input interface, source and destination address, source and destination port; and layer 3/4 protocols. Each entry also caches the destination interface and the gateway address - to update the destination link-layer address - to forward packets. The ttl and hoplimit fields are also decremented. Hence, flowtables provides an alternative path that allow packets to bypass the classic forwarding path. Flowtables reside in the ingress hook that is located before the prerouting hook. You can select which flows you want to offload through the flow expression from the forward chain. Flowtables are identified by their address family and their name. The address family must be one of ip, ip6, or inet. The inet address family is a dummy family which is used to create hybrid IPv4/IPv6 tables. When no address family is specified, ip is used by default. The priority can be a signed integer or filter which stands for 0. Addition and subtraction can be used to set relative priority, e.g. filter + 5 equals to 5. add Add a new flowtable for the given family with the given name. delete Delete the specified flowtable. destroy Delete the specified flowtable, it does not fail if it does not exist. list List all flowtables. LISTING list { secmarks | synproxys | flow tables | meters | hooks } [family] list { secmarks | synproxys | flow tables | meters | hooks } table [family] table list ct { timeout | expectation | helper | helpers } table [family] table Inspect configured objects. list hooks shows the full hook pipeline, including those registered by kernel modules, such as nf_conntrack. STATEFUL OBJECTS {add | delete | destroy | list | reset} counter [family] table object {add | delete | destroy | list | reset} quota [family] table object {add | delete | destroy | list} limit [family] table object delete counter [family] table handle handle delete quota [family] table handle handle delete limit [family] table handle handle destroy counter [family] table handle handle destroy quota [family] table handle handle destroy limit [family] table handle handle list counters [family] list quotas [family] list limits [family] reset counters [family] reset quotas [family] reset counters [family] table reset quotas [family] table Stateful objects are attached to tables and are identified by a unique name. They group stateful information from rules, to reference them in rules the keywords "type name" are used e.g. "counter name". add Add a new stateful object in the specified table. delete Delete the specified object. destroy Delete the specified object, it does not fail if it does not exist. list Display stateful information the object holds. reset List-and-reset stateful object. CT HELPER add ct helper [family] table name { type type protocol protocol ; [l3proto family ;] } delete ct helper [family] table name list ct helpers Ct helper is used to define connection tracking helpers that can then be used in combination with the ct helper set statement. type and protocol are mandatory, l3proto is derived from the table family by default, i.e. in the inet table the kernel will try to load both the ipv4 and ipv6 helper backends, if they are supported by the kernel. Table 12. conntrack helper specifications ┌──────────┬─────────────────────────┬──────────────────────────┐ │ Keyword │ Description │ Type │ ├──────────┼─────────────────────────┼──────────────────────────┤ │ │ │ │ │ type │ name of helper type │ quoted string (e.g. │ │ │ │ "ftp") │ ├──────────┼─────────────────────────┼──────────────────────────┤ │ │ │ │ │ protocol │ layer 4 protocol of the │ string (e.g. ip) │ │ │ helper │ │ ├──────────┼─────────────────────────┼──────────────────────────┤ │ │ │ │ │ l3proto │ layer 3 protocol of the │ address family (e.g. ip) │ │ │ helper │ │ ├──────────┼─────────────────────────┼──────────────────────────┤ │ │ │ │ │ comment │ per ct helper comment │ string │ │ │ field │ │ └──────────┴─────────────────────────┴──────────────────────────┘ defining and assigning ftp helper. Unlike iptables, helper assignment needs to be performed after the conntrack lookup has completed, for example with the default 0 hook priority. table inet myhelpers { ct helper ftp-standard { type "ftp" protocol tcp } chain prerouting { type filter hook prerouting priority filter; tcp dport 21 ct helper set "ftp-standard" } } CT TIMEOUT add ct timeout [family] table name { protocol protocol ; policy = { state: value [, ...] } ; [l3proto family ;] } delete ct timeout [family] table name list ct timeouts Ct timeout is used to update connection tracking timeout values.Timeout policies are assigned with the ct timeout set statement. protocol and policy are mandatory, l3proto is derived from the table family by default. Table 13. conntrack timeout specifications ┌──────────┬─────────────────────────┬──────────────────────────┐ │ Keyword │ Description │ Type │ ├──────────┼─────────────────────────┼──────────────────────────┤ │ │ │ │ │ protocol │ layer 4 protocol of the │ string (e.g. ip) │ │ │ timeout object │ │ ├──────────┼─────────────────────────┼──────────────────────────┤ │ │ │ │ │ state │ connection state name │ string (e.g. │ │ │ │ "established") │ ├──────────┼─────────────────────────┼──────────────────────────┤ │ │ │ │ │ value │ timeout value for │ unsigned integer │ │ │ connection state │ │ ├──────────┼─────────────────────────┼──────────────────────────┤ │ │ │ │ │ l3proto │ layer 3 protocol of the │ address family (e.g. ip) │ │ │ timeout object │ │ ├──────────┼─────────────────────────┼──────────────────────────┤ │ │ │ │ │ comment │ per ct timeout comment │ string │ │ │ field │ │ └──────────┴─────────────────────────┴──────────────────────────┘ tcp connection state names that can have a specific timeout value are: close, close_wait, established, fin_wait, last_ack, retrans, syn_recv, syn_sent, time_wait and unack. You can use sysctl -a |grep net.netfilter.nf_conntrack_tcp_timeout_ to view and change the system-wide defaults. ct timeout allows for flow-specific settings, without changing the global timeouts. For example, tcp port 53 could have much lower settings than other traffic. udp state names that can have a specific timeout value are replied and unreplied. defining and assigning ct timeout policy. table ip filter { ct timeout customtimeout { protocol tcp; l3proto ip policy = { established: 2m, close: 20s } } chain output { type filter hook output priority filter; policy accept; ct timeout set "customtimeout" } } testing the updated timeout policy. % conntrack -E It should display: [UPDATE] tcp 6 120 ESTABLISHED src=172.16.19.128 dst=172.16.19.1 sport=22 dport=41360 [UNREPLIED] src=172.16.19.1 dst=172.16.19.128 sport=41360 dport=22 CT EXPECTATION add ct expectation [family] table name { protocol protocol ; dport dport ; timeout timeout ; size size ; [*l3proto family ;] } delete ct expectation [family] table name list ct expectations Ct expectation is used to create connection expectations. Expectations are assigned with the ct expectation set statement. protocol, dport, timeout and size are mandatory, l3proto is derived from the table family by default. Table 14. conntrack expectation specifications ┌──────────┬─────────────────────────┬──────────────────────────┐ │ Keyword │ Description │ Type │ ├──────────┼─────────────────────────┼──────────────────────────┤ │ │ │ │ │ protocol │ layer 4 protocol of the │ string (e.g. ip) │ │ │ expectation object │ │ ├──────────┼─────────────────────────┼──────────────────────────┤ │ │ │ │ │ dport │ destination port of │ unsigned integer │ │ │ expected connection │ │ ├──────────┼─────────────────────────┼──────────────────────────┤ │ │ │ │ │ timeout │ timeout value for │ unsigned integer │ │ │ expectation │ │ ├──────────┼─────────────────────────┼──────────────────────────┤ │ │ │ │ │ size │ size value for │ unsigned integer │ │ │ expectation │ │ ├──────────┼─────────────────────────┼──────────────────────────┤ │ │ │ │ │ l3proto │ layer 3 protocol of the │ address family (e.g. ip) │ │ │ expectation object │ │ ├──────────┼─────────────────────────┼──────────────────────────┤ │ │ │ │ │ comment │ per ct expectation │ string │ │ │ comment field │ │ └──────────┴─────────────────────────┴──────────────────────────┘ defining and assigning ct expectation policy. table ip filter { ct expectation expect { protocol udp dport 9876 timeout 2m size 8 l3proto ip } chain input { type filter hook input priority filter; policy accept; ct expectation set "expect" } } COUNTER add counter [family] table name [{ [ packets packets bytes bytes ; ] [ comment comment ; }] delete counter [family] table name list counters Table 15. Counter specifications ┌─────────┬──────────────────────────┬──────────────────────┐ │ Keyword │ Description │ Type │ ├─────────┼──────────────────────────┼──────────────────────┤ │ │ │ │ │ packets │ initial count of packets │ unsigned integer (64 │ │ │ │ bit) │ ├─────────┼──────────────────────────┼──────────────────────┤ │ │ │ │ │ bytes │ initial count of bytes │ unsigned integer (64 │ │ │ │ bit) │ ├─────────┼──────────────────────────┼──────────────────────┤ │ │ │ │ │ comment │ per counter comment │ string │ │ │ field │ │ └─────────┴──────────────────────────┴──────────────────────┘ Using named counters. nft add counter filter http nft add rule filter input tcp dport 80 counter name \"http\" Using named counters with maps. nft add counter filter http nft add counter filter https nft add rule filter input counter name tcp dport map { 80 : \"http\", 443 : \"https\" } QUOTA add quota [family] table name { [over|until] bytes BYTE_UNIT [ used bytes BYTE_UNIT ] ; [ comment comment ; ] } BYTE_UNIT := bytes | kbytes | mbytes delete quota [family] table name list quotas Table 16. Quota specifications ┌─────────┬──────────────────────────┬─────────────────────────┐ │ Keyword │ Description │ Type │ ├─────────┼──────────────────────────┼─────────────────────────┤ │ │ │ │ │ quota │ quota limit, used as the │ Two arguments, unsigned │ │ │ quota name │ integer (64 bit) and │ │ │ │ string: bytes, kbytes, │ │ │ │ mbytes. "over" and │ │ │ │ "until" go before these │ │ │ │ arguments │ ├─────────┼──────────────────────────┼─────────────────────────┤ │ │ │ │ │ used │ initial value of used │ Two arguments, unsigned │ │ │ quota │ integer (64 bit) and │ │ │ │ string: bytes, kbytes, │ │ │ │ mbytes │ ├─────────┼──────────────────────────┼─────────────────────────┤ │ │ │ │ │ comment │ per quota comment field │ string │ └─────────┴──────────────────────────┴─────────────────────────┘ Using named quotas. nft add quota filter user123 { over 20 mbytes } nft add rule filter input ip saddr 192.168.10.123 quota name \"user123\" Using named quotas with maps. nft add quota filter user123 { over 20 mbytes } nft add quota filter user124 { over 20 mbytes } nft add rule filter input quota name ip saddr map { 192.168.10.123 : \"user123\", 192.168.10.124 : \"user124\" } EXPRESSIONS Expressions represent values, either constants like network addresses, port numbers, etc., or data gathered from the packet during ruleset evaluation. Expressions can be combined using binary, logical, relational and other types of expressions to form complex or relational (match) expressions. They are also used as arguments to certain types of operations, like NAT, packet marking etc. Each expression has a data type, which determines the size, parsing and representation of symbolic values and type compatibility with other expressions. DESCRIBE COMMAND describe expression | data type The describe command shows information about the type of an expression and its data type. A data type may also be given, in which nft will display more information about the type. The describe command. $ nft describe tcp flags payload expression, datatype tcp_flag (TCP flag) (basetype bitmask, integer), 8 bits predefined symbolic constants: fin 0x01 syn 0x02 rst 0x04 psh 0x08 ack 0x10 urg 0x20 ecn 0x40 cwr 0x80 DATA TYPES Data types determine the size, parsing and representation of symbolic values and type compatibility of expressions. A number of global data types exist, in addition some expression types define further data types specific to the expression type. Most data types have a fixed size, some however may have a dynamic size, f.i. the string type. Some types also have predefined symbolic constants. Those can be listed using the nft describe command: $ nft describe ct_state datatype ct_state (conntrack state) (basetype bitmask, integer), 32 bits pre-defined symbolic constants (in hexadecimal): invalid 0x00000001 new ... Types may be derived from lower order types, f.i. the IPv4 address type is derived from the integer type, meaning an IPv4 address can also be specified as an integer value. In certain contexts (set and map definitions), it is necessary to explicitly specify a data type. Each type has a name which is used for this. INTEGER TYPE ┌─────────┬─────────┬──────────┬───────────┐ │ Name │ Keyword │ Size │ Base type │ ├─────────┼─────────┼──────────┼───────────┤ │ │ │ │ │ │ Integer │ integer │ variable │ - │ └─────────┴─────────┴──────────┴───────────┘ The integer type is used for numeric values. It may be specified as a decimal, hexadecimal or octal number. The integer type does not have a fixed size, its size is determined by the expression for which it is used. BITMASK TYPE ┌─────────┬─────────┬──────────┬───────────┐ │ Name │ Keyword │ Size │ Base type │ ├─────────┼─────────┼──────────┼───────────┤ │ │ │ │ │ │ Bitmask │ bitmask │ variable │ integer │ └─────────┴─────────┴──────────┴───────────┘ The bitmask type (bitmask) is used for bitmasks. STRING TYPE ┌────────┬─────────┬──────────┬───────────┐ │ Name │ Keyword │ Size │ Base type │ ├────────┼─────────┼──────────┼───────────┤ │ │ │ │ │ │ String │ string │ variable │ - │ └────────┴─────────┴──────────┴───────────┘ The string type is used for character strings. A string begins with an alphabetic character (a-zA-Z) followed by zero or more alphanumeric characters or the characters /, -, _ and .. In addition, anything enclosed in double quotes (") is recognized as a string. String specification. # Interface name filter input iifname eth0 # Weird interface name filter input iifname "(eth0)" LINK LAYER ADDRESS TYPE ┌────────────────────┬─────────┬──────────┬───────────┐ │ Name │ Keyword │ Size │ Base type │ ├────────────────────┼─────────┼──────────┼───────────┤ │ │ │ │ │ │ Link layer address │ lladdr │ variable │ integer │ └────────────────────┴─────────┴──────────┴───────────┘ The link layer address type is used for link layer addresses. Link layer addresses are specified as a variable amount of groups of two hexadecimal digits separated using colons (:). Link layer address specification. # Ethernet destination MAC address filter input ether daddr 20:c9:d0:43:12:d9 IPV4 ADDRESS TYPE ┌──────────────┬───────────┬────────┬───────────┐ │ Name │ Keyword │ Size │ Base type │ ├──────────────┼───────────┼────────┼───────────┤ │ │ │ │ │ │ IPV4 address │ ipv4_addr │ 32 bit │ integer │ └──────────────┴───────────┴────────┴───────────┘ The IPv4 address type is used for IPv4 addresses. Addresses are specified in either dotted decimal, dotted hexadecimal, dotted octal, decimal, hexadecimal, octal notation or as a host name. A host name will be resolved using the standard system resolver. IPv4 address specification. # dotted decimal notation filter output ip daddr 127.0.0.1 # host name filter output ip daddr localhost IPV6 ADDRESS TYPE ┌──────────────┬───────────┬─────────┬───────────┐ │ Name │ Keyword │ Size │ Base type │ ├──────────────┼───────────┼─────────┼───────────┤ │ │ │ │ │ │ IPv6 address │ ipv6_addr │ 128 bit │ integer │ └──────────────┴───────────┴─────────┴───────────┘ The IPv6 address type is used for IPv6 addresses. Addresses are specified as a host name or as hexadecimal halfwords separated by colons. Addresses might be enclosed in square brackets ("[]") to differentiate them from port numbers. IPv6 address specification. # abbreviated loopback address filter output ip6 daddr ::1 IPv6 address specification with bracket notation. # without [] the port number (22) would be parsed as part of the # ipv6 address ip6 nat prerouting tcp dport 2222 dnat to [1ce::d0]:22 BOOLEAN TYPE ┌─────────┬─────────┬───────┬───────────┐ │ Name │ Keyword │ Size │ Base type │ ├─────────┼─────────┼───────┼───────────┤ │ │ │ │ │ │ Boolean │ boolean │ 1 bit │ integer │ └─────────┴─────────┴───────┴───────────┘ The boolean type is a syntactical helper type in userspace. Its use is in the right-hand side of a (typically implicit) relational expression to change the expression on the left-hand side into a boolean check (usually for existence). Table 17. The following keywords will automatically resolve into a boolean type with given value ┌─────────┬───────┐ │ Keyword │ Value │ ├─────────┼───────┤ │ │ │ │ exists │ 1 │ ├─────────┼───────┤ │ │ │ │ missing │ 0 │ └─────────┴───────┘ Table 18. expressions support a boolean comparison ┌────────────┬─────────────────────────────┐ │ Expression │ Behaviour │ ├────────────┼─────────────────────────────┤ │ │ │ │ fib │ Check route existence. │ ├────────────┼─────────────────────────────┤ │ │ │ │ exthdr │ Check IPv6 extension header │ │ │ existence. │ ├────────────┼─────────────────────────────┤ │ │ │ │ tcp option │ Check TCP option header │ │ │ existence. │ └────────────┴─────────────────────────────┘ Boolean specification. # match if route exists filter input fib daddr . iif oif exists # match only non-fragmented packets in IPv6 traffic filter input exthdr frag missing # match if TCP timestamp option is present filter input tcp option timestamp exists ICMP TYPE TYPE ┌───────────┬───────────┬───────┬───────────┐ │ Name │ Keyword │ Size │ Base type │ ├───────────┼───────────┼───────┼───────────┤ │ │ │ │ │ │ ICMP Type │ icmp_type │ 8 bit │ integer │ └───────────┴───────────┴───────┴───────────┘ The ICMP Type type is used to conveniently specify the ICMP header’s type field. Table 19. Keywords may be used when specifying the ICMP type ┌─────────────────────────┬───────┐ │ Keyword │ Value │ ├─────────────────────────┼───────┤ │ │ │ │ echo-reply │ 0 │ ├─────────────────────────┼───────┤ │ │ │ │ destination-unreachable │ 3 │ ├─────────────────────────┼───────┤ │ │ │ │ source-quench │ 4 │ ├─────────────────────────┼───────┤ │ │ │ │ redirect │ 5 │ ├─────────────────────────┼───────┤ │ │ │ │ echo-request │ 8 │ ├─────────────────────────┼───────┤ │ │ │ │ router-advertisement │ 9 │ ├─────────────────────────┼───────┤ │ │ │ │ router-solicitation │ 10 │ ├─────────────────────────┼───────┤ │ │ │ │ time-exceeded │ 11 │ ├─────────────────────────┼───────┤ │ │ │ │ parameter-problem │ 12 │ ├─────────────────────────┼───────┤ │ │ │ │ timestamp-request │ 13 │ ├─────────────────────────┼───────┤ │ │ │ │ timestamp-reply │ 14 │ ├─────────────────────────┼───────┤ │ │ │ │ info-request │ 15 │ ├─────────────────────────┼───────┤ │ │ │ │ info-reply │ 16 │ ├─────────────────────────┼───────┤ │ │ │ │ address-mask-request │ 17 │ ├─────────────────────────┼───────┤ │ │ │ │ address-mask-reply │ 18 │ └─────────────────────────┴───────┘ ICMP Type specification. # match ping packets filter output icmp type { echo-request, echo-reply } ICMP CODE TYPE ┌───────────┬───────────┬───────┬───────────┐ │ Name │ Keyword │ Size │ Base type │ ├───────────┼───────────┼───────┼───────────┤ │ │ │ │ │ │ ICMP Code │ icmp_code │ 8 bit │ integer │ └───────────┴───────────┴───────┴───────────┘ The ICMP Code type is used to conveniently specify the ICMP header’s code field. Table 20. Keywords may be used when specifying the ICMP code ┌──────────────────┬───────┐ │ Keyword │ Value │ ├──────────────────┼───────┤ │ │ │ │ net-unreachable │ 0 │ ├──────────────────┼───────┤ │ │ │ │ host-unreachable │ 1 │ ├──────────────────┼───────┤ │ │ │ │ prot-unreachable │ 2 │ ├──────────────────┼───────┤ │ │ │ │ port-unreachable │ 3 │ ├──────────────────┼───────┤ │ │ │ │ frag-needed │ 4 │ ├──────────────────┼───────┤ │ │ │ │ net-prohibited │ 9 │ ├──────────────────┼───────┤ │ │ │ │ host-prohibited │ 10 │ ├──────────────────┼───────┤ │ │ │ │ admin-prohibited │ 13 │ └──────────────────┴───────┘ ICMPV6 TYPE TYPE ┌─────────────┬────────────┬───────┬───────────┐ │ Name │ Keyword │ Size │ Base type │ ├─────────────┼────────────┼───────┼───────────┤ │ │ │ │ │ │ ICMPv6 Type │ icmpx_code │ 8 bit │ integer │ └─────────────┴────────────┴───────┴───────────┘ The ICMPv6 Type type is used to conveniently specify the ICMPv6 header’s type field. Table 21. keywords may be used when specifying the ICMPv6 type: ┌─────────────────────────┬───────┐ │ Keyword │ Value │ ├─────────────────────────┼───────┤ │ │ │ │ destination-unreachable │ 1 │ ├─────────────────────────┼───────┤ │ │ │ │ packet-too-big │ 2 │ ├─────────────────────────┼───────┤ │ │ │ │ time-exceeded │ 3 │ ├─────────────────────────┼───────┤ │ │ │ │ parameter-problem │ 4 │ ├─────────────────────────┼───────┤ │ │ │ │ echo-request │ 128 │ ├─────────────────────────┼───────┤ │ │ │ │ echo-reply │ 129 │ ├─────────────────────────┼───────┤ │ │ │ │ mld-listener-query │ 130 │ ├─────────────────────────┼───────┤ │ │ │ │ mld-listener-report │ 131 │ ├─────────────────────────┼───────┤ │ │ │ │ mld-listener-done │ 132 │ ├─────────────────────────┼───────┤ │ │ │ │ mld-listener-reduction │ 132 │ ├─────────────────────────┼───────┤ │ │ │ │ nd-router-solicit │ 133 │ ├─────────────────────────┼───────┤ │ │ │ │ nd-router-advert │ 134 │ ├─────────────────────────┼───────┤ │ │ │ │ nd-neighbor-solicit │ 135 │ ├─────────────────────────┼───────┤ │ │ │ │ nd-neighbor-advert │ 136 │ ├─────────────────────────┼───────┤ │ │ │ │ nd-redirect │ 137 │ ├─────────────────────────┼───────┤ │ │ │ │ router-renumbering │ 138 │ ├─────────────────────────┼───────┤ │ │ │ │ ind-neighbor-solicit │ 141 │ ├─────────────────────────┼───────┤ │ │ │ │ ind-neighbor-advert │ 142 │ ├─────────────────────────┼───────┤ │ │ │ │ mld2-listener-report │ 143 │ └─────────────────────────┴───────┘ ICMPv6 Type specification. # match ICMPv6 ping packets filter output icmpv6 type { echo-request, echo-reply } ICMPV6 CODE TYPE ┌─────────────┬─────────────┬───────┬───────────┐ │ Name │ Keyword │ Size │ Base type │ ├─────────────┼─────────────┼───────┼───────────┤ │ │ │ │ │ │ ICMPv6 Code │ icmpv6_code │ 8 bit │ integer │ └─────────────┴─────────────┴───────┴───────────┘ The ICMPv6 Code type is used to conveniently specify the ICMPv6 header’s code field. Table 22. keywords may be used when specifying the ICMPv6 code ┌──────────────────┬───────┐ │ Keyword │ Value │ ├──────────────────┼───────┤ │ │ │ │ no-route │ 0 │ ├──────────────────┼───────┤ │ │ │ │ admin-prohibited │ 1 │ ├──────────────────┼───────┤ │ │ │ │ addr-unreachable │ 3 │ ├──────────────────┼───────┤ │ │ │ │ port-unreachable │ 4 │ ├──────────────────┼───────┤ │ │ │ │ policy-fail │ 5 │ ├──────────────────┼───────┤ │ │ │ │ reject-route │ 6 │ └──────────────────┴───────┘ ICMPVX CODE TYPE ┌─────────────┬─────────────┬───────┬───────────┐ │ Name │ Keyword │ Size │ Base type │ ├─────────────┼─────────────┼───────┼───────────┤ │ │ │ │ │ │ ICMPvX Code │ icmpv6_type │ 8 bit │ integer │ └─────────────┴─────────────┴───────┴───────────┘ The ICMPvX Code type abstraction is a set of values which overlap between ICMP and ICMPv6 Code types to be used from the inet family. Table 23. keywords may be used when specifying the ICMPvX code ┌──────────────────┬───────┐ │ Keyword │ Value │ ├──────────────────┼───────┤ │ │ │ │ no-route │ 0 │ ├──────────────────┼───────┤ │ │ │ │ port-unreachable │ 1 │ ├──────────────────┼───────┤ │ │ │ │ host-unreachable │ 2 │ ├──────────────────┼───────┤ │ │ │ │ admin-prohibited │ 3 │ └──────────────────┴───────┘ CONNTRACK TYPES Table 24. overview of types used in ct expression and statement ┌─────────────────────┬───────────┬─────────┬───────────┐ │ Name │ Keyword │ Size │ Base type │ ├─────────────────────┼───────────┼─────────┼───────────┤ │ │ │ │ │ │ conntrack state │ ct_state │ 4 byte │ bitmask │ ├─────────────────────┼───────────┼─────────┼───────────┤ │ │ │ │ │ │ conntrack direction │ ct_dir │ 8 bit │ integer │ ├─────────────────────┼───────────┼─────────┼───────────┤ │ │ │ │ │ │ conntrack status │ ct_status │ 4 byte │ bitmask │ ├─────────────────────┼───────────┼─────────┼───────────┤ │ │ │ │ │ │ conntrack event │ ct_event │ 4 byte │ bitmask │ │ bits │ │ │ │ ├─────────────────────┼───────────┼─────────┼───────────┤ │ │ │ │ │ │ conntrack label │ ct_label │ 128 bit │ bitmask │ └─────────────────────┴───────────┴─────────┴───────────┘ For each of the types above, keywords are available for convenience: Table 25. conntrack state (ct_state) ┌─────────────┬───────┐ │ Keyword │ Value │ ├─────────────┼───────┤ │ │ │ │ invalid │ 1 │ ├─────────────┼───────┤ │ │ │ │ established │ 2 │ ├─────────────┼───────┤ │ │ │ │ related │ 4 │ ├─────────────┼───────┤ │ │ │ │ new │ 8 │ ├─────────────┼───────┤ │ │ │ │ untracked │ 64 │ └─────────────┴───────┘ Table 26. conntrack direction (ct_dir) ┌──────────┬───────┐ │ Keyword │ Value │ ├──────────┼───────┤ │ │ │ │ original │ 0 │ ├──────────┼───────┤ │ │ │ │ reply │ 1 │ └──────────┴───────┘ Table 27. conntrack status (ct_status) ┌────────────┬───────┐ │ Keyword │ Value │ ├────────────┼───────┤ │ │ │ │ expected │ 1 │ ├────────────┼───────┤ │ │ │ │ seen-reply │ 2 │ ├────────────┼───────┤ │ │ │ │ assured │ 4 │ ├────────────┼───────┤ │ │ │ │ confirmed │ 8 │ ├────────────┼───────┤ │ │ │ │ snat │ 16 │ ├────────────┼───────┤ │ │ │ │ dnat │ 32 │ ├────────────┼───────┤ │ │ │ │ dying │ 512 │ └────────────┴───────┘ Table 28. conntrack event bits (ct_event) ┌───────────┬───────┐ │ Keyword │ Value │ ├───────────┼───────┤ │ │ │ │ new │ 1 │ ├───────────┼───────┤ │ │ │ │ related │ 2 │ ├───────────┼───────┤ │ │ │ │ destroy │ 4 │ ├───────────┼───────┤ │ │ │ │ reply │ 8 │ ├───────────┼───────┤ │ │ │ │ assured │ 16 │ ├───────────┼───────┤ │ │ │ │ protoinfo │ 32 │ ├───────────┼───────┤ │ │ │ │ helper │ 64 │ ├───────────┼───────┤ │ │ │ │ mark │ 128 │ ├───────────┼───────┤ │ │ │ │ seqadj │ 256 │ ├───────────┼───────┤ │ │ │ │ secmark │ 512 │ ├───────────┼───────┤ │ │ │ │ label │ 1024 │ └───────────┴───────┘ Possible keywords for conntrack label type (ct_label) are read at runtime from /etc/connlabel.conf. DCCP PKTTYPE TYPE ┌──────────────────┬──────────────┬───────┬───────────┐ │ Name │ Keyword │ Size │ Base type │ ├──────────────────┼──────────────┼───────┼───────────┤ │ │ │ │ │ │ DCCP packet type │ dccp_pkttype │ 4 bit │ integer │ └──────────────────┴──────────────┴───────┴───────────┘ The DCCP packet type abstracts the different legal values of the respective four bit field in the DCCP header, as stated by RFC4340. Note that possible values 10-15 are considered reserved and therefore not allowed to be used. In iptables' dccp match, these values are aliased INVALID. With nftables, one may simply match on the numeric value range, i.e. 10-15. Table 29. keywords may be used when specifying the DCCP packet type ┌──────────┬───────┐ │ Keyword │ Value │ ├──────────┼───────┤ │ │ │ │ request │ 0 │ ├──────────┼───────┤ │ │ │ │ response │ 1 │ ├──────────┼───────┤ │ │ │ │ data │ 2 │ ├──────────┼───────┤ │ │ │ │ ack │ 3 │ ├──────────┼───────┤ │ │ │ │ dataack │ 4 │ ├──────────┼───────┤ │ │ │ │ closereq │ 5 │ ├──────────┼───────┤ │ │ │ │ close │ 6 │ ├──────────┼───────┤ │ │ │ │ reset │ 7 │ ├──────────┼───────┤ │ │ │ │ sync │ 8 │ ├──────────┼───────┤ │ │ │ │ syncack │ 9 │ └──────────┴───────┘ PRIMARY EXPRESSIONS The lowest order expression is a primary expression, representing either a constant or a single datum from a packet’s payload, meta data or a stateful module. META EXPRESSIONS meta {length | nfproto | l4proto | protocol | priority} [meta] {mark | iif | iifname | iiftype | oif | oifname | oiftype | skuid | skgid | nftrace | rtclassid | ibrname | obrname | pkttype | cpu | iifgroup | oifgroup | cgroup | random | ipsec | iifkind | oifkind | time | hour | day } A meta expression refers to meta data associated with a packet. There are two types of meta expressions: unqualified and qualified meta expressions. Qualified meta expressions require the meta keyword before the meta key, unqualified meta expressions can be specified by using the meta key directly or as qualified meta expressions. Meta l4proto is useful to match a particular transport protocol that is part of either an IPv4 or IPv6 packet. It will also skip any IPv6 extension headers present in an IPv6 packet. meta iif, oif, iifname and oifname are used to match the interface a packet arrived on or is about to be sent out on. iif and oif are used to match on the interface index, whereas iifname and oifname are used to match on the interface name. This is not the same — assuming the rule filter input meta iif "foo" Then this rule can only be added if the interface "foo" exists. Also, the rule will continue to match even if the interface "foo" is renamed to "bar". This is because internally the interface index is used. In case of dynamically created interfaces, such as tun/tap or dialup interfaces (ppp for example), it might be better to use iifname or oifname instead. In these cases, the name is used so the interface doesn’t have to exist to add such a rule, it will stop matching if the interface gets renamed and it will match again in case interface gets deleted and later a new interface with the same name is created. Like with iptables, wildcard matching on interface name prefixes is available for iifname and oifname matches by appending an asterisk (*) character. Note however that unlike iptables, nftables does not accept interface names consisting of the wildcard character only - users are supposed to just skip those always matching expressions. In order to match on literal asterisk character, one may escape it using backslash (\). Table 30. Meta expression types ┌───────────┬──────────────────────────┬─────────────────────┐ │ Keyword │ Description │ Type │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ length │ Length of the packet in │ integer (32-bit) │ │ │ bytes │ │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ nfproto │ real hook protocol │ integer (32 bit) │ │ │ family, useful only in │ │ │ │ inet table │ │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ l4proto │ layer 4 protocol, skips │ integer (8 bit) │ │ │ ipv6 extension headers │ │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ protocol │ EtherType protocol value │ ether_type │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ priority │ TC packet priority │ tc_handle │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ mark │ Packet mark │ mark │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ iif │ Input interface index │ iface_index │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ iifname │ Input interface name │ ifname │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ iiftype │ Input interface type │ iface_type │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ oif │ Output interface index │ iface_index │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ oifname │ Output interface name │ ifname │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ oiftype │ Output interface │ iface_type │ │ │ hardware type │ │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ sdif │ Slave device input │ iface_index │ │ │ interface index │ │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ sdifname │ Slave device interface │ ifname │ │ │ name │ │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ skuid │ UID associated with │ uid │ │ │ originating socket │ │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ skgid │ GID associated with │ gid │ │ │ originating socket │ │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ rtclassid │ Routing realm │ realm │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ ibrname │ Input bridge interface │ ifname │ │ │ name │ │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ obrname │ Output bridge interface │ ifname │ │ │ name │ │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ pkttype │ packet type │ pkt_type │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ cpu │ cpu number processing │ integer (32 bit) │ │ │ the packet │ │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ iifgroup │ incoming device group │ devgroup │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ oifgroup │ outgoing device group │ devgroup │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ cgroup │ control group id │ integer (32 bit) │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ random │ pseudo-random number │ integer (32 bit) │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ ipsec │ true if packet was ipsec │ boolean (1 bit) │ │ │ encrypted │ │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ iifkind │ Input interface kind │ │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ oifkind │ Output interface kind │ │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ time │ Absolute time of packet │ Integer (32 bit) or │ │ │ reception │ string │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ day │ Day of week │ Integer (8 bit) or │ │ │ │ string │ ├───────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ hour │ Hour of day │ String │ └───────────┴──────────────────────────┴─────────────────────┘ Table 31. Meta expression specific types ┌───────────────┬──────────────────────────────────┐ │ Type │ Description │ ├───────────────┼──────────────────────────────────┤ │ │ │ │ iface_index │ Interface index (32 bit number). │ │ │ Can be specified numerically or │ │ │ as name of an existing │ │ │ interface. │ ├───────────────┼──────────────────────────────────┤ │ │ │ │ ifname │ Interface name (16 byte string). │ │ │ Does not have to exist. │ ├───────────────┼──────────────────────────────────┤ │ │ │ │ iface_type │ Interface type (16 bit number). │ ├───────────────┼──────────────────────────────────┤ │ │ │ │ uid │ User ID (32 bit number). Can be │ │ │ specified numerically or as user │ │ │ name. │ ├───────────────┼──────────────────────────────────┤ │ │ │ │ gid │ Group ID (32 bit number). Can be │ │ │ specified numerically or as │ │ │ group name. │ ├───────────────┼──────────────────────────────────┤ │ │ │ │ realm │ Routing Realm (32 bit number). │ │ │ Can be specified numerically or │ │ │ as symbolic name defined in │ │ │ /etc/iproute2/rt_realms. │ ├───────────────┼──────────────────────────────────┤ │ │ │ │ devgroup_type │ Device group (32 bit number). │ │ │ Can be specified numerically or │ │ │ as symbolic name defined in │ │ │ /etc/iproute2/group. │ ├───────────────┼──────────────────────────────────┤ │ │ │ │ pkt_type │ Packet type: host (addressed to │ │ │ local host), broadcast (to all), │ │ │ multicast (to group), other │ │ │ (addressed to another host). │ ├───────────────┼──────────────────────────────────┤ │ │ │ │ ifkind │ Interface kind (16 byte string). │ │ │ See TYPES in ip-link(8) for a │ │ │ list. │ ├───────────────┼──────────────────────────────────┤ │ │ │ │ time │ Either an integer or a date in │ │ │ ISO format. For example: │ │ │ "2019-06-06 17:00". Hour and │ │ │ seconds are optional and can be │ │ │ omitted if desired. If omitted, │ │ │ midnight will be assumed. The │ │ │ following three would be │ │ │ equivalent: "2019-06-06", │ │ │ "2019-06-06 00:00" and │ │ │ "2019-06-06 00:00:00". When an │ │ │ integer is given, it is assumed │ │ │ to be a UNIX timestamp. │ ├───────────────┼──────────────────────────────────┤ │ │ │ │ day │ Either a day of week ("Monday", │ │ │ "Tuesday", etc.), or an integer │ │ │ between 0 and 6. Strings are │ │ │ matched case-insensitively, and │ │ │ a full match is not expected │ │ │ (e.g. "Mon" would match │ │ │ "Monday"). When an integer is │ │ │ given, 0 is Sunday and 6 is │ │ │ Saturday. │ ├───────────────┼──────────────────────────────────┤ │ │ │ │ hour │ A string representing an hour in │ │ │ 24-hour format. Seconds can │ │ │ optionally be specified. For │ │ │ example, 17:00 and 17:00:00 │ │ │ would be equivalent. │ └───────────────┴──────────────────────────────────┘ Using meta expressions. # qualified meta expression filter output meta oif eth0 filter forward meta iifkind { "tun", "veth" } # unqualified meta expression filter output oif eth0 # incoming packet was subject to ipsec processing raw prerouting meta ipsec exists accept SOCKET EXPRESSION socket {transparent | mark | wildcard} socket cgroupv2 level NUM Socket expression can be used to search for an existing open TCP/UDP socket and its attributes that can be associated with a packet. It looks for an established or non-zero bound listening socket (possibly with a non-local address). You can also use it to match on the socket cgroupv2 at a given ancestor level, e.g. if the socket belongs to cgroupv2 a/b, ancestor level 1 checks for a matching on cgroup a and ancestor level 2 checks for a matching on cgroup b. Table 32. Available socket attributes ┌─────────────┬──────────────────────────┬─────────────────┐ │ Name │ Description │ Type │ ├─────────────┼──────────────────────────┼─────────────────┤ │ │ │ │ │ transparent │ Value of the │ boolean (1 bit) │ │ │ IP_TRANSPARENT socket │ │ │ │ option in the found │ │ │ │ socket. It can be 0 or │ │ │ │ 1. │ │ ├─────────────┼──────────────────────────┼─────────────────┤ │ │ │ │ │ mark │ Value of the socket mark │ mark │ │ │ (SOL_SOCKET, SO_MARK). │ │ ├─────────────┼──────────────────────────┼─────────────────┤ │ │ │ │ │ wildcard │ Indicates whether the │ boolean (1 bit) │ │ │ socket is wildcard-bound │ │ │ │ (e.g. 0.0.0.0 or ::0). │ │ ├─────────────┼──────────────────────────┼─────────────────┤ │ │ │ │ │ cgroupv2 │ cgroup version 2 for │ cgroupv2 │ │ │ this socket (path from │ │ │ │ /sys/fs/cgroup) │ │ └─────────────┴──────────────────────────┴─────────────────┘ Using socket expression. # Mark packets that correspond to a transparent socket. "socket wildcard 0" # means that zero-bound listener sockets are NOT matched (which is usually # exactly what you want). table inet x { chain y { type filter hook prerouting priority mangle; policy accept; socket transparent 1 socket wildcard 0 mark set 0x00000001 accept } } # Trace packets that corresponds to a socket with a mark value of 15 table inet x { chain y { type filter hook prerouting priority mangle; policy accept; socket mark 0x0000000f nftrace set 1 } } # Set packet mark to socket mark table inet x { chain y { type filter hook prerouting priority mangle; policy accept; tcp dport 8080 mark set socket mark } } # Count packets for cgroupv2 "user.slice" at level 1 table inet x { chain y { type filter hook input priority filter; policy accept; socket cgroupv2 level 1 "user.slice" counter } } OSF EXPRESSION osf [ttl {loose | skip}] {name | version} The osf expression does passive operating system fingerprinting. This expression compares some data (Window Size, MSS, options and their order, DF, and others) from packets with the SYN bit set. Table 33. Available osf attributes ┌─────────┬──────────────────────────┬────────┐ │ Name │ Description │ Type │ ├─────────┼──────────────────────────┼────────┤ │ │ │ │ │ ttl │ Do TTL checks on the │ string │ │ │ packet to determine the │ │ │ │ operating system. │ │ ├─────────┼──────────────────────────┼────────┤ │ │ │ │ │ version │ Do OS version checks on │ │ │ │ the packet. │ │ ├─────────┼──────────────────────────┼────────┤ │ │ │ │ │ name │ Name of the OS signature │ string │ │ │ to match. All signatures │ │ │ │ can be found at pf.os │ │ │ │ file. Use "unknown" for │ │ │ │ OS signatures that the │ │ │ │ expression could not │ │ │ │ detect. │ │ └─────────┴──────────────────────────┴────────┘ Available ttl values. If no TTL attribute is passed, make a true IP header and fingerprint TTL true comparison. This generally works for LANs. * loose: Check if the IP header's TTL is less than the fingerprint one. Works for globally-routable addresses. * skip: Do not compare the TTL at all. Using osf expression. # Accept packets that match the "Linux" OS genre signature without comparing TTL. table inet x { chain y { type filter hook input priority filter; policy accept; osf ttl skip name "Linux" } } FIB EXPRESSIONS fib {saddr | daddr | mark | iif | oif} [. ...] {oif | oifname | type} A fib expression queries the fib (forwarding information base) to obtain information such as the output interface index a particular address would use. The input is a tuple of elements that is used as input to the fib lookup functions. Table 34. fib expression specific types ┌─────────┬────────────────────────┬──────────────────┐ │ Keyword │ Description │ Type │ ├─────────┼────────────────────────┼──────────────────┤ │ │ │ │ │ oif │ Output interface index │ integer (32 bit) │ ├─────────┼────────────────────────┼──────────────────┤ │ │ │ │ │ oifname │ Output interface name │ string │ ├─────────┼────────────────────────┼──────────────────┤ │ │ │ │ │ type │ Address type │ fib_addrtype │ └─────────┴────────────────────────┴──────────────────┘ Use nft describe fib_addrtype to get a list of all address types. Using fib expressions. # drop packets without a reverse path filter prerouting fib saddr . iif oif missing drop In this example, 'saddr . iif' looks up routing information based on the source address and the input interface. oif picks the output interface index from the routing information. If no route was found for the source address/input interface combination, the output interface index is zero. In case the input interface is specified as part of the input key, the output interface index is always the same as the input interface index or zero. If only 'saddr oif' is given, then oif can be any interface index or zero. # drop packets to address not configured on incoming interface filter prerouting fib daddr . iif type != { local, broadcast, multicast } drop # perform lookup in a specific 'blackhole' table (0xdead, needs ip appropriate ip rule) filter prerouting meta mark set 0xdead fib daddr . mark type vmap { blackhole : drop, prohibit : jump prohibited, unreachable : drop } ROUTING EXPRESSIONS rt [ip | ip6] {classid | nexthop | mtu | ipsec} A routing expression refers to routing data associated with a packet. Table 35. Routing expression types ┌─────────┬──────────────────────────┬─────────────────────┐ │ Keyword │ Description │ Type │ ├─────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ classid │ Routing realm │ realm │ ├─────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ nexthop │ Routing nexthop │ ipv4_addr/ipv6_addr │ ├─────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ mtu │ TCP maximum segment size │ integer (16 bit) │ │ │ of route │ │ ├─────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ ipsec │ route via ipsec tunnel │ boolean │ │ │ or transport │ │ └─────────┴──────────────────────────┴─────────────────────┘ Table 36. Routing expression specific types ┌───────┬─────────────────────────────────┐ │ Type │ Description │ ├───────┼─────────────────────────────────┤ │ │ │ │ realm │ Routing Realm (32 bit number). │ │ │ Can be specified numerically or │ │ │ as symbolic name defined in │ │ │ /etc/iproute2/rt_realms. │ └───────┴─────────────────────────────────┘ Using routing expressions. # IP family independent rt expression filter output rt classid 10 # IP family dependent rt expressions ip filter output rt nexthop 192.168.0.1 ip6 filter output rt nexthop fd00::1 inet filter output rt ip nexthop 192.168.0.1 inet filter output rt ip6 nexthop fd00::1 # outgoing packet will be encapsulated/encrypted by ipsec filter output rt ipsec exists IPSEC EXPRESSIONS ipsec {in | out} [ spnum NUM ] {reqid | spi} ipsec {in | out} [ spnum NUM ] {ip | ip6} {saddr | daddr} An ipsec expression refers to ipsec data associated with a packet. The in or out keyword needs to be used to specify if the expression should examine inbound or outbound policies. The in keyword can be used in the prerouting, input and forward hooks. The out keyword applies to forward, output and postrouting hooks. The optional keyword spnum can be used to match a specific state in a chain, it defaults to 0. Table 37. Ipsec expression types ┌─────────┬──────────────────────────┬─────────────────────┐ │ Keyword │ Description │ Type │ ├─────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ reqid │ Request ID │ integer (32 bit) │ ├─────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ spi │ Security Parameter Index │ integer (32 bit) │ ├─────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ saddr │ Source address of the │ ipv4_addr/ipv6_addr │ │ │ tunnel │ │ ├─────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ daddr │ Destination address of │ ipv4_addr/ipv6_addr │ │ │ the tunnel │ │ └─────────┴──────────────────────────┴─────────────────────┘ Note: When using xfrm_interface, this expression is not useable in output hook as the plain packet does not traverse it with IPsec info attached - use a chain in postrouting hook instead. NUMGEN EXPRESSION numgen {inc | random} mod NUM [ offset NUM ] Create a number generator. The inc or random keywords control its operation mode: In inc mode, the last returned value is simply incremented. In random mode, a new random number is returned. The value after mod keyword specifies an upper boundary (read: modulus) which is not reached by returned numbers. The optional offset allows one to increment the returned value by a fixed offset. A typical use-case for numgen is load-balancing: Using numgen expression. # round-robin between 192.168.10.100 and 192.168.20.200: add rule nat prerouting dnat to numgen inc mod 2 map \ { 0 : 192.168.10.100, 1 : 192.168.20.200 } # probability-based with odd bias using intervals: add rule nat prerouting dnat to numgen random mod 10 map \ { 0-2 : 192.168.10.100, 3-9 : 192.168.20.200 } HASH EXPRESSIONS jhash {ip saddr | ip6 daddr | tcp dport | udp sport | ether saddr} [. ...] mod NUM [ seed NUM ] [ offset NUM ] symhash mod NUM [ offset NUM ] Use a hashing function to generate a number. The functions available are jhash, known as Jenkins Hash, and symhash, for Symmetric Hash. The jhash requires an expression to determine the parameters of the packet header to apply the hashing, concatenations are possible as well. The value after mod keyword specifies an upper boundary (read: modulus) which is not reached by returned numbers. The optional seed is used to specify an init value used as seed in the hashing function. The optional offset allows one to increment the returned value by a fixed offset. A typical use-case for jhash and symhash is load-balancing: Using hash expressions. # load balance based on source ip between 2 ip addresses: add rule nat prerouting dnat to jhash ip saddr mod 2 map \ { 0 : 192.168.10.100, 1 : 192.168.20.200 } # symmetric load balancing between 2 ip addresses: add rule nat prerouting dnat to symhash mod 2 map \ { 0 : 192.168.10.100, 1 : 192.168.20.200 } PAYLOAD EXPRESSIONS Payload expressions refer to data from the packet’s payload. ETHERNET HEADER EXPRESSION ether {daddr | saddr | type} Table 38. Ethernet header expression types ┌─────────┬─────────────────────────┬────────────┐ │ Keyword │ Description │ Type │ ├─────────┼─────────────────────────┼────────────┤ │ │ │ │ │ daddr │ Destination MAC address │ ether_addr │ ├─────────┼─────────────────────────┼────────────┤ │ │ │ │ │ saddr │ Source MAC address │ ether_addr │ ├─────────┼─────────────────────────┼────────────┤ │ │ │ │ │ type │ EtherType │ ether_type │ └─────────┴─────────────────────────┴────────────┘ VLAN HEADER EXPRESSION vlan {id | dei | pcp | type} The vlan expression is used to match on the vlan header fields. This expression will not work in the ip, ip6 and inet families, unless the vlan interface is configured with the reorder_hdr off setting. The default is reorder_hdr on which will automatically remove the vlan tag from the packet. See ip-link(8) for more information. For these families its easier to match the vlan interface name instead, using the meta iif or meta iifname expression. Table 39. VLAN header expression ┌─────────┬─────────────────────────┬──────────────────┐ │ Keyword │ Description │ Type │ ├─────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ id │ VLAN ID (VID) │ integer (12 bit) │ ├─────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ dei │ Drop Eligible Indicator │ integer (1 bit) │ ├─────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ pcp │ Priority code point │ integer (3 bit) │ ├─────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ type │ EtherType │ ether_type │ └─────────┴─────────────────────────┴──────────────────┘ ARP HEADER EXPRESSION arp {htype | ptype | hlen | plen | operation | saddr { ip | ether } | daddr { ip | ether } Table 40. ARP header expression ┌─────────────┬─────────────────────────┬──────────────────┐ │ Keyword │ Description │ Type │ ├─────────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ htype │ ARP hardware type │ integer (16 bit) │ ├─────────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ ptype │ EtherType │ ether_type │ ├─────────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ hlen │ Hardware address len │ integer (8 bit) │ ├─────────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ plen │ Protocol address len │ integer (8 bit) │ ├─────────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ operation │ Operation │ arp_op │ ├─────────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ saddr ether │ Ethernet sender address │ ether_addr │ ├─────────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ daddr ether │ Ethernet target address │ ether_addr │ ├─────────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ saddr ip │ IPv4 sender address │ ipv4_addr │ ├─────────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ daddr ip │ IPv4 target address │ ipv4_addr │ └─────────────┴─────────────────────────┴──────────────────┘ IPV4 HEADER EXPRESSION ip {version | hdrlength | dscp | ecn | length | id | frag-off | ttl | protocol | checksum | saddr | daddr } Table 41. IPv4 header expression ┌───────────┬─────────────────────────┬───────────────────────┐ │ Keyword │ Description │ Type │ ├───────────┼─────────────────────────┼───────────────────────┤ │ │ │ │ │ version │ IP header version (4) │ integer (4 bit) │ ├───────────┼─────────────────────────┼───────────────────────┤ │ │ │ │ │ hdrlength │ IP header length │ integer (4 bit) FIXME │ │ │ including options │ scaling │ ├───────────┼─────────────────────────┼───────────────────────┤ │ │ │ │ │ dscp │ Differentiated Services │ dscp │ │ │ Code Point │ │ ├───────────┼─────────────────────────┼───────────────────────┤ │ │ │ │ │ ecn │ Explicit Congestion │ ecn │ │ │ Notification │ │ ├───────────┼─────────────────────────┼───────────────────────┤ │ │ │ │ │ length │ Total packet length │ integer (16 bit) │ ├───────────┼─────────────────────────┼───────────────────────┤ │ │ │ │ │ id │ IP ID │ integer (16 bit) │ ├───────────┼─────────────────────────┼───────────────────────┤ │ │ │ │ │ frag-off │ Fragment offset │ integer (16 bit) │ ├───────────┼─────────────────────────┼───────────────────────┤ │ │ │ │ │ ttl │ Time to live │ integer (8 bit) │ ├───────────┼─────────────────────────┼───────────────────────┤ │ │ │ │ │ protocol │ Upper layer protocol │ inet_proto │ ├───────────┼─────────────────────────┼───────────────────────┤ │ │ │ │ │ checksum │ IP header checksum │ integer (16 bit) │ ├───────────┼─────────────────────────┼───────────────────────┤ │ │ │ │ │ saddr │ Source address │ ipv4_addr │ ├───────────┼─────────────────────────┼───────────────────────┤ │ │ │ │ │ daddr │ Destination address │ ipv4_addr │ └───────────┴─────────────────────────┴───────────────────────┘ Careful with matching on ip length: If GRO/GSO is enabled, then the Linux kernel might aggregate several packets into one big packet that is larger than MTU. Moreover, if GRO/GSO maximum size is larger than 65535 (see man ip-link(8), specifically gro_ipv6_max_size and gso_ipv6_max_size), then ip length might be 0 for such jumbo packets. meta length allows you to match on the packet length including the IP header size. If you want to perform heuristics on the ip length field, then disable GRO/GSO. ICMP HEADER EXPRESSION icmp {type | code | checksum | id | sequence | gateway | mtu} This expression refers to ICMP header fields. When using it in inet, bridge or netdev families, it will cause an implicit dependency on IPv4 to be created. To match on unusual cases like ICMP over IPv6, one has to add an explicit meta protocol ip6 match to the rule. Table 42. ICMP header expression ┌──────────┬─────────────────────────┬──────────────────┐ │ Keyword │ Description │ Type │ ├──────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ type │ ICMP type field │ icmp_type │ ├──────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ code │ ICMP code field │ integer (8 bit) │ ├──────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ checksum │ ICMP checksum field │ integer (16 bit) │ ├──────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ id │ ID of echo │ integer (16 bit) │ │ │ request/response │ │ ├──────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ sequence │ sequence number of echo │ integer (16 bit) │ │ │ request/response │ │ ├──────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ gateway │ gateway of redirects │ integer (32 bit) │ ├──────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ mtu │ MTU of path MTU │ integer (16 bit) │ │ │ discovery │ │ └──────────┴─────────────────────────┴──────────────────┘ IGMP HEADER EXPRESSION igmp {type | mrt | checksum | group} This expression refers to IGMP header fields. When using it in inet, bridge or netdev families, it will cause an implicit dependency on IPv4 to be created. To match on unusual cases like IGMP over IPv6, one has to add an explicit meta protocol ip6 match to the rule. Table 43. IGMP header expression ┌──────────┬───────────────────────┬──────────────────┐ │ Keyword │ Description │ Type │ ├──────────┼───────────────────────┼──────────────────┤ │ │ │ │ │ type │ IGMP type field │ igmp_type │ ├──────────┼───────────────────────┼──────────────────┤ │ │ │ │ │ mrt │ IGMP maximum response │ integer (8 bit) │ │ │ time field │ │ ├──────────┼───────────────────────┼──────────────────┤ │ │ │ │ │ checksum │ IGMP checksum field │ integer (16 bit) │ ├──────────┼───────────────────────┼──────────────────┤ │ │ │ │ │ group │ Group address │ integer (32 bit) │ └──────────┴───────────────────────┴──────────────────┘ IPV6 HEADER EXPRESSION ip6 {version | dscp | ecn | flowlabel | length | nexthdr | hoplimit | saddr | daddr} This expression refers to the ipv6 header fields. Caution when using ip6 nexthdr, the value only refers to the next header, i.e. ip6 nexthdr tcp will only match if the ipv6 packet does not contain any extension headers. Packets that are fragmented or e.g. contain a routing extension headers will not be matched. Please use meta l4proto if you wish to match the real transport header and ignore any additional extension headers instead. Table 44. IPv6 header expression ┌───────────┬─────────────────────────┬──────────────────┐ │ Keyword │ Description │ Type │ ├───────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ version │ IP header version (6) │ integer (4 bit) │ ├───────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ dscp │ Differentiated Services │ dscp │ │ │ Code Point │ │ ├───────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ ecn │ Explicit Congestion │ ecn │ │ │ Notification │ │ ├───────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ flowlabel │ Flow label │ integer (20 bit) │ ├───────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ length │ Payload length │ integer (16 bit) │ ├───────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ nexthdr │ Nexthdr protocol │ inet_proto │ ├───────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ hoplimit │ Hop limit │ integer (8 bit) │ ├───────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ saddr │ Source address │ ipv6_addr │ ├───────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ daddr │ Destination address │ ipv6_addr │ └───────────┴─────────────────────────┴──────────────────┘ Careful with matching on ip6 length: If GRO/GSO is enabled, then the Linux kernel might aggregate several packets into one big packet that is larger than MTU. Moreover, if GRO/GSO maximum size is larger than 65535 (see man ip-link(8), specifically gro_ipv6_max_size and gso_ipv6_max_size), then ip6 length might be 0 for such jumbo packets. meta length allows you to match on the packet length including the IP header size. If you want to perform heuristics on the ip6 length field, then disable GRO/GSO. Using ip6 header expressions. # matching if first extension header indicates a fragment ip6 nexthdr ipv6-frag ICMPV6 HEADER EXPRESSION icmpv6 {type | code | checksum | parameter-problem | packet-too-big | id | sequence | max-delay | taddr | daddr} This expression refers to ICMPv6 header fields. When using it in inet, bridge or netdev families, it will cause an implicit dependency on IPv6 to be created. To match on unusual cases like ICMPv6 over IPv4, one has to add an explicit meta protocol ip match to the rule. Table 45. ICMPv6 header expression ┌───────────────────┬──────────────────────────┬──────────────────┐ │ Keyword │ Description │ Type │ ├───────────────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ type │ ICMPv6 type field │ icmpv6_type │ ├───────────────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ code │ ICMPv6 code field │ integer (8 bit) │ ├───────────────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ checksum │ ICMPv6 checksum field │ integer (16 bit) │ ├───────────────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ parameter-problem │ pointer to problem │ integer (32 bit) │ ├───────────────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ packet-too-big │ oversized MTU │ integer (32 bit) │ ├───────────────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ id │ ID of echo │ integer (16 bit) │ │ │ request/response │ │ ├───────────────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ sequence │ sequence number of echo │ integer (16 bit) │ │ │ request/response │ │ ├───────────────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ max-delay │ maximum response delay │ integer (16 bit) │ │ │ of MLD queries │ │ ├───────────────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ taddr │ target address of │ ipv6_addr │ │ │ neighbor solicit/advert, │ │ │ │ redirect or MLD │ │ ├───────────────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ daddr │ destination address of │ ipv6_addr │ │ │ redirect │ │ └───────────────────┴──────────────────────────┴──────────────────┘ TCP HEADER EXPRESSION tcp {sport | dport | sequence | ackseq | doff | reserved | flags | window | checksum | urgptr} Table 46. TCP header expression ┌──────────┬────────────────────────┬───────────────────────┐ │ Keyword │ Description │ Type │ ├──────────┼────────────────────────┼───────────────────────┤ │ │ │ │ │ sport │ Source port │ inet_service │ ├──────────┼────────────────────────┼───────────────────────┤ │ │ │ │ │ dport │ Destination port │ inet_service │ ├──────────┼────────────────────────┼───────────────────────┤ │ │ │ │ │ sequence │ Sequence number │ integer (32 bit) │ ├──────────┼────────────────────────┼───────────────────────┤ │ │ │ │ │ ackseq │ Acknowledgement number │ integer (32 bit) │ ├──────────┼────────────────────────┼───────────────────────┤ │ │ │ │ │ doff │ Data offset │ integer (4 bit) FIXME │ │ │ │ scaling │ ├──────────┼────────────────────────┼───────────────────────┤ │ │ │ │ │ reserved │ Reserved area │ integer (4 bit) │ ├──────────┼────────────────────────┼───────────────────────┤ │ │ │ │ │ flags │ TCP flags │ tcp_flag │ ├──────────┼────────────────────────┼───────────────────────┤ │ │ │ │ │ window │ Window │ integer (16 bit) │ ├──────────┼────────────────────────┼───────────────────────┤ │ │ │ │ │ checksum │ Checksum │ integer (16 bit) │ ├──────────┼────────────────────────┼───────────────────────┤ │ │ │ │ │ urgptr │ Urgent pointer │ integer (16 bit) │ └──────────┴────────────────────────┴───────────────────────┘ UDP HEADER EXPRESSION udp {sport | dport | length | checksum} Table 47. UDP header expression ┌──────────┬─────────────────────┬──────────────────┐ │ Keyword │ Description │ Type │ ├──────────┼─────────────────────┼──────────────────┤ │ │ │ │ │ sport │ Source port │ inet_service │ ├──────────┼─────────────────────┼──────────────────┤ │ │ │ │ │ dport │ Destination port │ inet_service │ ├──────────┼─────────────────────┼──────────────────┤ │ │ │ │ │ length │ Total packet length │ integer (16 bit) │ ├──────────┼─────────────────────┼──────────────────┤ │ │ │ │ │ checksum │ Checksum │ integer (16 bit) │ └──────────┴─────────────────────┴──────────────────┘ UDP-LITE HEADER EXPRESSION udplite {sport | dport | checksum} Table 48. UDP-Lite header expression ┌──────────┬──────────────────┬──────────────────┐ │ Keyword │ Description │ Type │ ├──────────┼──────────────────┼──────────────────┤ │ │ │ │ │ sport │ Source port │ inet_service │ ├──────────┼──────────────────┼──────────────────┤ │ │ │ │ │ dport │ Destination port │ inet_service │ ├──────────┼──────────────────┼──────────────────┤ │ │ │ │ │ checksum │ Checksum │ integer (16 bit) │ └──────────┴──────────────────┴──────────────────┘ SCTP HEADER EXPRESSION sctp {sport | dport | vtag | checksum} sctp chunk CHUNK [ FIELD ] CHUNK := data | init | init-ack | sack | heartbeat | heartbeat-ack | abort | shutdown | shutdown-ack | error | cookie-echo | cookie-ack | ecne | cwr | shutdown-complete | asconf-ack | forward-tsn | asconf FIELD := COMMON_FIELD | DATA_FIELD | INIT_FIELD | INIT_ACK_FIELD | SACK_FIELD | SHUTDOWN_FIELD | ECNE_FIELD | CWR_FIELD | ASCONF_ACK_FIELD | FORWARD_TSN_FIELD | ASCONF_FIELD COMMON_FIELD := type | flags | length DATA_FIELD := tsn | stream | ssn | ppid INIT_FIELD := init-tag | a-rwnd | num-outbound-streams | num-inbound-streams | initial-tsn INIT_ACK_FIELD := INIT_FIELD SACK_FIELD := cum-tsn-ack | a-rwnd | num-gap-ack-blocks | num-dup-tsns SHUTDOWN_FIELD := cum-tsn-ack ECNE_FIELD := lowest-tsn CWR_FIELD := lowest-tsn ASCONF_ACK_FIELD := seqno FORWARD_TSN_FIELD := new-cum-tsn ASCONF_FIELD := seqno Table 49. SCTP header expression ┌──────────┬────────────────────────┬────────────────────────┐ │ Keyword │ Description │ Type │ ├──────────┼────────────────────────┼────────────────────────┤ │ │ │ │ │ sport │ Source port │ inet_service │ ├──────────┼────────────────────────┼────────────────────────┤ │ │ │ │ │ dport │ Destination port │ inet_service │ ├──────────┼────────────────────────┼────────────────────────┤ │ │ │ │ │ vtag │ Verification Tag │ integer (32 bit) │ ├──────────┼────────────────────────┼────────────────────────┤ │ │ │ │ │ checksum │ Checksum │ integer (32 bit) │ ├──────────┼────────────────────────┼────────────────────────┤ │ │ │ │ │ chunk │ Search chunk in packet │ without FIELD, boolean │ │ │ │ indicating existence │ └──────────┴────────────────────────┴────────────────────────┘ Table 50. SCTP chunk fields ┌──────────────────────┬───────────────┬────────────────────┬─────────────────────┐ │ Name │ Width in bits │ Chunk │ Notes │ ├──────────────────────┼───────────────┼────────────────────┼─────────────────────┤ │ │ │ │ │ │ type │ 8 │ all │ not useful, defined │ │ │ │ │ by chunk type │ ├──────────────────────┼───────────────┼────────────────────┼─────────────────────┤ │ │ │ │ │ │ flags │ 8 │ all │ semantics defined │ │ │ │ │ on per-chunk basis │ ├──────────────────────┼───────────────┼────────────────────┼─────────────────────┤ │ │ │ │ │ │ length │ 16 │ all │ length of this │ │ │ │ │ chunk in bytes │ │ │ │ │ excluding padding │ ├──────────────────────┼───────────────┼────────────────────┼─────────────────────┤ │ │ │ │ │ │ tsn │ 32 │ data │ transmission │ │ │ │ │ sequence number │ ├──────────────────────┼───────────────┼────────────────────┼─────────────────────┤ │ │ │ │ │ │ stream │ 16 │ data │ stream identifier │ ├──────────────────────┼───────────────┼────────────────────┼─────────────────────┤ │ │ │ │ │ │ ssn │ 16 │ data │ stream sequence │ │ │ │ │ number │ ├──────────────────────┼───────────────┼────────────────────┼─────────────────────┤ │ │ │ │ │ │ ppid │ 32 │ data │ payload protocol │ │ │ │ │ identifier │ ├──────────────────────┼───────────────┼────────────────────┼─────────────────────┤ │ │ │ │ │ │ init-tag │ 32 │ init, init-ack │ initiate tag │ ├──────────────────────┼───────────────┼────────────────────┼─────────────────────┤ │ │ │ │ │ │ a-rwnd │ 32 │ init, init-ack, │ advertised receiver │ │ │ │ sack │ window credit │ ├──────────────────────┼───────────────┼────────────────────┼─────────────────────┤ │ │ │ │ │ │ num-outbound-streams │ 16 │ init, init-ack │ number of outbound │ │ │ │ │ streams │ ├──────────────────────┼───────────────┼────────────────────┼─────────────────────┤ │ │ │ │ │ │ num-inbound-streams │ 16 │ init, init-ack │ number of inbound │ │ │ │ │ streams │ ├──────────────────────┼───────────────┼────────────────────┼─────────────────────┤ │ │ │ │ │ │ initial-tsn │ 32 │ init, init-ack │ initial transmit │ │ │ │ │ sequence number │ ├──────────────────────┼───────────────┼────────────────────┼─────────────────────┤ │ │ │ │ │ │ cum-tsn-ack │ 32 │ sack, shutdown │ cumulative │ │ │ │ │ transmission │ │ │ │ │ sequence number │ │ │ │ │ acknowledged │ ├──────────────────────┼───────────────┼────────────────────┼─────────────────────┤ │ │ │ │ │ │ num-gap-ack-blocks │ 16 │ sack │ number of Gap Ack │ │ │ │ │ Blocks included │ ├──────────────────────┼───────────────┼────────────────────┼─────────────────────┤ │ │ │ │ │ │ num-dup-tsns │ 16 │ sack │ number of duplicate │ │ │ │ │ transmission │ │ │ │ │ sequence numbers │ │ │ │ │ received │ ├──────────────────────┼───────────────┼────────────────────┼─────────────────────┤ │ │ │ │ │ │ lowest-tsn │ 32 │ ecne, cwr │ lowest transmission │ │ │ │ │ sequence number │ ├──────────────────────┼───────────────┼────────────────────┼─────────────────────┤ │ │ │ │ │ │ seqno │ 32 │ asconf-ack, asconf │ sequence number │ ├──────────────────────┼───────────────┼────────────────────┼─────────────────────┤ │ │ │ │ │ │ new-cum-tsn │ 32 │ forward-tsn │ new cumulative │ │ │ │ │ transmission │ │ │ │ │ sequence number │ └──────────────────────┴───────────────┴────────────────────┴─────────────────────┘ DCCP HEADER EXPRESSION dccp {sport | dport | type} Table 51. DCCP header expression ┌─────────┬──────────────────┬──────────────┐ │ Keyword │ Description │ Type │ ├─────────┼──────────────────┼──────────────┤ │ │ │ │ │ sport │ Source port │ inet_service │ ├─────────┼──────────────────┼──────────────┤ │ │ │ │ │ dport │ Destination port │ inet_service │ ├─────────┼──────────────────┼──────────────┤ │ │ │ │ │ type │ Packet type │ dccp_pkttype │ └─────────┴──────────────────┴──────────────┘ AUTHENTICATION HEADER EXPRESSION ah {nexthdr | hdrlength | reserved | spi | sequence} Table 52. AH header expression ┌───────────┬──────────────────────────┬──────────────────┐ │ Keyword │ Description │ Type │ ├───────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ nexthdr │ Next header protocol │ inet_proto │ ├───────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ hdrlength │ AH Header length │ integer (8 bit) │ ├───────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ reserved │ Reserved area │ integer (16 bit) │ ├───────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ spi │ Security Parameter Index │ integer (32 bit) │ ├───────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ sequence │ Sequence number │ integer (32 bit) │ └───────────┴──────────────────────────┴──────────────────┘ ENCRYPTED SECURITY PAYLOAD HEADER EXPRESSION esp {spi | sequence} Table 53. ESP header expression ┌──────────┬──────────────────────────┬──────────────────┐ │ Keyword │ Description │ Type │ ├──────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ spi │ Security Parameter Index │ integer (32 bit) │ ├──────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ sequence │ Sequence number │ integer (32 bit) │ └──────────┴──────────────────────────┴──────────────────┘ IPCOMP HEADER EXPRESSION comp {nexthdr | flags | cpi} Table 54. IPComp header expression ┌─────────┬───────────────────────┬──────────────────┐ │ Keyword │ Description │ Type │ ├─────────┼───────────────────────┼──────────────────┤ │ │ │ │ │ nexthdr │ Next header protocol │ inet_proto │ ├─────────┼───────────────────────┼──────────────────┤ │ │ │ │ │ flags │ Flags │ bitmask │ ├─────────┼───────────────────────┼──────────────────┤ │ │ │ │ │ cpi │ compression Parameter │ integer (16 bit) │ │ │ Index │ │ └─────────┴───────────────────────┴──────────────────┘ GRE HEADER EXPRESSION gre {flags | version | protocol} gre ip {version | hdrlength | dscp | ecn | length | id | frag-off | ttl | protocol | checksum | saddr | daddr } gre ip6 {version | dscp | ecn | flowlabel | length | nexthdr | hoplimit | saddr | daddr} The gre expression is used to match on the gre header fields. This expression also allows to match on the IPv4 or IPv6 packet within the gre header. Table 55. GRE header expression ┌──────────┬──────────────────────────┬──────────────────┐ │ Keyword │ Description │ Type │ ├──────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ flags │ checksum, routing, key, │ integer (5 bit) │ │ │ sequence and strict │ │ │ │ source route flags │ │ ├──────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ version │ gre version field, 0 for │ integer (3 bit) │ │ │ GRE and 1 for PPTP │ │ ├──────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ protocol │ EtherType of │ integer (16 bit) │ │ │ encapsulated packet │ │ └──────────┴──────────────────────────┴──────────────────┘ Matching inner IPv4 destination address encapsulated in gre. netdev filter ingress gre ip daddr 9.9.9.9 counter GENEVE HEADER EXPRESSION geneve {vni | flags} geneve ether {daddr | saddr | type} geneve vlan {id | dei | pcp | type} geneve ip {version | hdrlength | dscp | ecn | length | id | frag-off | ttl | protocol | checksum | saddr | daddr } geneve ip6 {version | dscp | ecn | flowlabel | length | nexthdr | hoplimit | saddr | daddr} geneve tcp {sport | dport | sequence | ackseq | doff | reserved | flags | window | checksum | urgptr} geneve udp {sport | dport | length | checksum} The geneve expression is used to match on the geneve header fields. The geneve header encapsulates a ethernet frame within a udp packet. This expression requires that you restrict the matching to udp packets (usually at port 6081 according to IANA-assigned ports). Table 56. GENEVE header expression ┌──────────┬──────────────────────────┬──────────────────┐ │ Keyword │ Description │ Type │ ├──────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ protocol │ EtherType of │ integer (16 bit) │ │ │ encapsulated packet │ │ ├──────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ vni │ Virtual Network ID (VNI) │ integer (24 bit) │ └──────────┴──────────────────────────┴──────────────────┘ Matching inner TCP destination port encapsulated in geneve. netdev filter ingress udp dport 4789 geneve tcp dport 80 counter GRETAP HEADER EXPRESSION gretap {vni | flags} gretap ether {daddr | saddr | type} gretap vlan {id | dei | pcp | type} gretap ip {version | hdrlength | dscp | ecn | length | id | frag-off | ttl | protocol | checksum | saddr | daddr } gretap ip6 {version | dscp | ecn | flowlabel | length | nexthdr | hoplimit | saddr | daddr} gretap tcp {sport | dport | sequence | ackseq | doff | reserved | flags | window | checksum | urgptr} gretap udp {sport | dport | length | checksum} The gretap expression is used to match on the encapsulated ethernet frame within the gre header. Use the gre expression to match on the gre header fields. Matching inner TCP destination port encapsulated in gretap. netdev filter ingress gretap tcp dport 80 counter VXLAN HEADER EXPRESSION vxlan {vni | flags} vxlan ether {daddr | saddr | type} vxlan vlan {id | dei | pcp | type} vxlan ip {version | hdrlength | dscp | ecn | length | id | frag-off | ttl | protocol | checksum | saddr | daddr } vxlan ip6 {version | dscp | ecn | flowlabel | length | nexthdr | hoplimit | saddr | daddr} vxlan tcp {sport | dport | sequence | ackseq | doff | reserved | flags | window | checksum | urgptr} vxlan udp {sport | dport | length | checksum} The vxlan expression is used to match on the vxlan header fields. The vxlan header encapsulates a ethernet frame within a udp packet. This expression requires that you restrict the matching to udp packets (usually at port 4789 according to IANA-assigned ports). Table 57. VXLAN header expression ┌─────────┬──────────────────────────┬──────────────────┐ │ Keyword │ Description │ Type │ ├─────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ flags │ vxlan flags │ integer (8 bit) │ ├─────────┼──────────────────────────┼──────────────────┤ │ │ │ │ │ vni │ Virtual Network ID (VNI) │ integer (24 bit) │ └─────────┴──────────────────────────┴──────────────────┘ Matching inner TCP destination port encapsulated in vxlan. netdev filter ingress udp dport 4789 vxlan tcp dport 80 counter ARP HEADER EXPRESSION arp {htype | ptype | hlen | plen | operation | saddr { ip | ether } | daddr { ip | ether } Table 58. ARP header expression ┌─────────────┬─────────────────────────┬──────────────────┐ │ Keyword │ Description │ Type │ ├─────────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ htype │ ARP hardware type │ integer (16 bit) │ ├─────────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ ptype │ EtherType │ ether_type │ ├─────────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ hlen │ Hardware address len │ integer (8 bit) │ ├─────────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ plen │ Protocol address len │ integer (8 bit) │ ├─────────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ operation │ Operation │ arp_op │ ├─────────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ saddr ether │ Ethernet sender address │ ether_addr │ ├─────────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ daddr ether │ Ethernet target address │ ether_addr │ ├─────────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ saddr ip │ IPv4 sender address │ ipv4_addr │ ├─────────────┼─────────────────────────┼──────────────────┤ │ │ │ │ │ daddr ip │ IPv4 target address │ ipv4_addr │ └─────────────┴─────────────────────────┴──────────────────┘ RAW PAYLOAD EXPRESSION @base,offset,length The raw payload expression instructs to load length bits starting at offset bits. Bit 0 refers to the very first bit — in the C programming language, this corresponds to the topmost bit, i.e. 0x80 in case of an octet. They are useful to match headers that do not have a human-readable template expression yet. Note that nft will not add dependencies for Raw payload expressions. If you e.g. want to match protocol fields of a transport header with protocol number 5, you need to manually exclude packets that have a different transport header, for instance by using meta l4proto 5 before the raw expression. Table 59. Supported payload protocol bases ┌──────┬──────────────────────────────────┐ │ Base │ Description │ ├──────┼──────────────────────────────────┤ │ │ │ │ ll │ Link layer, for example the │ │ │ Ethernet header │ ├──────┼──────────────────────────────────┤ │ │ │ │ nh │ Network header, for example IPv4 │ │ │ or IPv6 │ ├──────┼──────────────────────────────────┤ │ │ │ │ th │ Transport Header, for example │ │ │ TCP │ ├──────┼──────────────────────────────────┤ │ │ │ │ ih │ Inner Header / Payload, i.e. │ │ │ after the L4 transport level │ │ │ header │ └──────┴──────────────────────────────────┘ Matching destination port of both UDP and TCP. inet filter input meta l4proto {tcp, udp} @th,16,16 { 53, 80 } The above can also be written as inet filter input meta l4proto {tcp, udp} th dport { 53, 80 } it is more convenient, but like the raw expression notation no dependencies are created or checked. It is the users responsibility to restrict matching to those header types that have a notion of ports. Otherwise, rules using raw expressions will errnously match unrelated packets, e.g. mis-interpreting ESP packets SPI field as a port. Rewrite arp packet target hardware address if target protocol address matches a given address. input meta iifname enp2s0 arp ptype 0x0800 arp htype 1 arp hlen 6 arp plen 4 @nh,192,32 0xc0a88f10 @nh,144,48 set 0x112233445566 accept EXTENSION HEADER EXPRESSIONS Extension header expressions refer to data from variable-sized protocol headers, such as IPv6 extension headers, TCP options and IPv4 options. nftables currently supports matching (finding) a given ipv6 extension header, TCP option or IPv4 option. hbh {nexthdr | hdrlength} frag {nexthdr | frag-off | more-fragments | id} rt {nexthdr | hdrlength | type | seg-left} dst {nexthdr | hdrlength} mh {nexthdr | hdrlength | checksum | type} srh {flags | tag | sid | seg-left} tcp option {eol | nop | maxseg | window | sack-perm | sack | sack0 | sack1 | sack2 | sack3 | timestamp} tcp_option_field ip option { lsrr | ra | rr | ssrr } ip_option_field The following syntaxes are valid only in a relational expression with boolean type on right-hand side for checking header existence only: exthdr {hbh | frag | rt | dst | mh} tcp option {eol | nop | maxseg | window | sack-perm | sack | sack0 | sack1 | sack2 | sack3 | timestamp} ip option { lsrr | ra | rr | ssrr } dccp option dccp_option_type Table 60. IPv6 extension headers ┌─────────┬────────────────────────┐ │ Keyword │ Description │ ├─────────┼────────────────────────┤ │ │ │ │ hbh │ Hop by Hop │ ├─────────┼────────────────────────┤ │ │ │ │ rt │ Routing Header │ ├─────────┼────────────────────────┤ │ │ │ │ frag │ Fragmentation header │ ├─────────┼────────────────────────┤ │ │ │ │ dst │ dst options │ ├─────────┼────────────────────────┤ │ │ │ │ mh │ Mobility Header │ ├─────────┼────────────────────────┤ │ │ │ │ srh │ Segment Routing Header │ └─────────┴────────────────────────┘ Table 61. TCP Options ┌───────────┬──────────────────────────┬──────────────────────┐ │ Keyword │ Description │ TCP option fields │ ├───────────┼──────────────────────────┼──────────────────────┤ │ │ │ │ │ eol │ End if option list │ - │ ├───────────┼──────────────────────────┼──────────────────────┤ │ │ │ │ │ nop │ 1 Byte TCP Nop padding │ - │ │ │ option │ │ ├───────────┼──────────────────────────┼──────────────────────┤ │ │ │ │ │ maxseg │ TCP Maximum Segment Size │ length, size │ ├───────────┼──────────────────────────┼──────────────────────┤ │ │ │ │ │ window │ TCP Window Scaling │ length, count │ ├───────────┼──────────────────────────┼──────────────────────┤ │ │ │ │ │ sack-perm │ TCP SACK permitted │ length │ ├───────────┼──────────────────────────┼──────────────────────┤ │ │ │ │ │ sack │ TCP Selective │ length, left, right │ │ │ Acknowledgement (alias │ │ │ │ of block 0) │ │ ├───────────┼──────────────────────────┼──────────────────────┤ │ │ │ │ │ sack0 │ TCP Selective │ length, left, right │ │ │ Acknowledgement (block │ │ │ │ 0) │ │ ├───────────┼──────────────────────────┼──────────────────────┤ │ │ │ │ │ sack1 │ TCP Selective │ length, left, right │ │ │ Acknowledgement (block │ │ │ │ 1) │ │ ├───────────┼──────────────────────────┼──────────────────────┤ │ │ │ │ │ sack2 │ TCP Selective │ length, left, right │ │ │ Acknowledgement (block │ │ │ │ 2) │ │ ├───────────┼──────────────────────────┼──────────────────────┤ │ │ │ │ │ sack3 │ TCP Selective │ length, left, right │ │ │ Acknowledgement (block │ │ │ │ 3) │ │ ├───────────┼──────────────────────────┼──────────────────────┤ │ │ │ │ │ timestamp │ TCP Timestamps │ length, tsval, tsecr │ └───────────┴──────────────────────────┴──────────────────────┘ TCP option matching also supports raw expression syntax to access arbitrary options: tcp option tcp option @number,offset,length Table 62. IP Options ┌─────────┬─────────────────────┬─────────────────────────┐ │ Keyword │ Description │ IP option fields │ ├─────────┼─────────────────────┼─────────────────────────┤ │ │ │ │ │ lsrr │ Loose Source Route │ type, length, ptr, addr │ ├─────────┼─────────────────────┼─────────────────────────┤ │ │ │ │ │ ra │ Router Alert │ type, length, value │ ├─────────┼─────────────────────┼─────────────────────────┤ │ │ │ │ │ rr │ Record Route │ type, length, ptr, addr │ ├─────────┼─────────────────────┼─────────────────────────┤ │ │ │ │ │ ssrr │ Strict Source Route │ type, length, ptr, addr │ └─────────┴─────────────────────┴─────────────────────────┘ finding TCP options. filter input tcp option sack-perm exists counter matching TCP options. filter input tcp option maxseg size lt 536 matching IPv6 exthdr. ip6 filter input frag more-fragments 1 counter finding IP option. filter input ip option lsrr exists counter finding DCCP option. filter input dccp option 40 exists counter CONNTRACK EXPRESSIONS Conntrack expressions refer to meta data of the connection tracking entry associated with a packet. There are three types of conntrack expressions. Some conntrack expressions require the flow direction before the conntrack key, others must be used directly because they are direction agnostic. The packets, bytes and avgpkt keywords can be used with or without a direction. If the direction is omitted, the sum of the original and the reply direction is returned. The same is true for the zone, if a direction is given, the zone is only matched if the zone id is tied to the given direction. ct {state | direction | status | mark | expiration | helper | label | count | id} ct [original | reply] {l3proto | protocol | bytes | packets | avgpkt | zone} ct {original | reply} {proto-src | proto-dst} ct {original | reply} {ip | ip6} {saddr | daddr} The conntrack-specific types in this table are described in the sub-section CONNTRACK TYPES above. Table 63. Conntrack expressions ┌────────────┬──────────────────────────┬─────────────────────┐ │ Keyword │ Description │ Type │ ├────────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ state │ State of the connection │ ct_state │ ├────────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ direction │ Direction of the packet │ ct_dir │ │ │ relative to the │ │ │ │ connection │ │ ├────────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ status │ Status of the connection │ ct_status │ ├────────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ mark │ Connection mark │ mark │ ├────────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ expiration │ Connection expiration │ time │ │ │ time │ │ ├────────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ helper │ Helper associated with │ string │ │ │ the connection │ │ ├────────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ label │ Connection tracking │ ct_label │ │ │ label bit or symbolic │ │ │ │ name defined in │ │ │ │ connlabel.conf in the │ │ │ │ nftables include path │ │ ├────────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ l3proto │ Layer 3 protocol of the │ nf_proto │ │ │ connection │ │ ├────────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ saddr │ Source address of the │ ipv4_addr/ipv6_addr │ │ │ connection for the given │ │ │ │ direction │ │ ├────────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ daddr │ Destination address of │ ipv4_addr/ipv6_addr │ │ │ the connection for the │ │ │ │ given direction │ │ ├────────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ protocol │ Layer 4 protocol of the │ inet_proto │ │ │ connection for the given │ │ │ │ direction │ │ ├────────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ proto-src │ Layer 4 protocol source │ integer (16 bit) │ │ │ for the given direction │ │ ├────────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ proto-dst │ Layer 4 protocol │ integer (16 bit) │ │ │ destination for the │ │ │ │ given direction │ │ ├────────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ packets │ packet count seen in the │ integer (64 bit) │ │ │ given direction or sum │ │ │ │ of original and reply │ │ ├────────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ bytes │ byte count seen, see │ integer (64 bit) │ │ │ description for packets │ │ │ │ keyword │ │ ├────────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ avgpkt │ average bytes per │ integer (64 bit) │ │ │ packet, see description │ │ │ │ for packets keyword │ │ ├────────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ zone │ conntrack zone │ integer (16 bit) │ ├────────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ count │ number of current │ integer (32 bit) │ │ │ connections │ │ ├────────────┼──────────────────────────┼─────────────────────┤ │ │ │ │ │ id │ Connection id │ ct_id │ └────────────┴──────────────────────────┴─────────────────────┘ restrict the number of parallel connections to a server. nft add set filter ssh_flood '{ type ipv4_addr; flags dynamic; }' nft add rule filter input tcp dport 22 add @ssh_flood '{ ip saddr ct count over 2 }' reject STATEMENTS Statements represent actions to be performed. They can alter control flow (return, jump to a different chain, accept or drop the packet) or can perform actions, such as logging, rejecting a packet, etc. Statements exist in two kinds. Terminal statements unconditionally terminate evaluation of the current rule, non-terminal statements either only conditionally or never terminate evaluation of the current rule, in other words, they are passive from the ruleset evaluation perspective. There can be an arbitrary amount of non-terminal statements in a rule, but only a single terminal statement as the final statement. VERDICT STATEMENT The verdict statement alters control flow in the ruleset and issues policy decisions for packets. {accept | drop | queue | continue | return} {jump | goto} chain accept and drop are absolute verdicts — they terminate ruleset evaluation immediately. accept Terminate ruleset evaluation and accept the packet. The packet can still be dropped later by another hook, for instance accept in the forward hook still allows one to drop the packet later in the postrouting hook, or another forward base chain that has a higher priority number and is evaluated afterwards in the processing pipeline. drop Terminate ruleset evaluation and drop the packet. The drop occurs instantly, no further chains or hooks are evaluated. It is not possible to accept the packet in a later chain again, as those are not evaluated anymore for the packet. queue Terminate ruleset evaluation and queue the packet to userspace. Userspace must provide a drop or accept verdict. In case of accept, processing resumes with the next base chain hook, not the rule following the queue verdict. continue Continue ruleset evaluation with the next rule. This is the default behaviour in case a rule issues no verdict. return Return from the current chain and continue evaluation at the next rule in the last chain. If issued in a base chain, it is equivalent to the base chain policy. jump chain Continue evaluation at the first rule in chain. The current position in the ruleset is pushed to a call stack and evaluation will continue there when the new chain is entirely evaluated or a return verdict is issued. In case an absolute verdict is issued by a rule in the chain, ruleset evaluation terminates immediately and the specific action is taken. goto chain Similar to jump, but the current position is not pushed to the call stack, meaning that after the new chain evaluation will continue at the last chain instead of the one containing the goto statement. Using verdict statements. # process packets from eth0 and the internal network in from_lan # chain, drop all packets from eth0 with different source addresses. filter input iif eth0 ip saddr 192.168.0.0/24 jump from_lan filter input iif eth0 drop PAYLOAD STATEMENT payload_expression set value The payload statement alters packet content. It can be used for example to set ip DSCP (diffserv) header field or ipv6 flow labels. route some packets instead of bridging. # redirect tcp:http from 192.160.0.0/16 to local machine for routing instead of bridging # assumes 00:11:22:33:44:55 is local MAC address. bridge input meta iif eth0 ip saddr 192.168.0.0/16 tcp dport 80 meta pkttype set unicast ether daddr set 00:11:22:33:44:55 Set IPv4 DSCP header field. ip forward ip dscp set 42 EXTENSION HEADER STATEMENT extension_header_expression set value The extension header statement alters packet content in variable-sized headers. This can currently be used to alter the TCP Maximum segment size of packets, similar to the TCPMSS target in iptables. change tcp mss. tcp flags syn tcp option maxseg size set 1360 # set a size based on route information: tcp flags syn tcp option maxseg size set rt mtu You can also remove tcp options via reset keyword. remove tcp option. tcp flags syn reset tcp option sack-perm LOG STATEMENT log [prefix quoted_string] [level syslog-level] [flags log-flags] log group nflog_group [prefix quoted_string] [queue-threshold value] [snaplen size] log level audit The log statement enables logging of matching packets. When this statement is used from a rule, the Linux kernel will print some information on all matching packets, such as header fields, via the kernel log (where it can be read with dmesg(1) or read in the syslog). In the second form of invocation (if nflog_group is specified), the Linux kernel will pass the packet to nfnetlink_log which will send the log through a netlink socket to the specified group. One userspace process may subscribe to the group to receive the logs, see man(8) ulogd for the Netfilter userspace log daemon and libnetfilter_log documentation for details in case you would like to develop a custom program to digest your logs. In the third form of invocation (if level audit is specified), the Linux kernel writes a message into the audit buffer suitably formatted for reading with auditd. Therefore no further formatting options (such as prefix or flags) are allowed in this mode. This is a non-terminating statement, so the rule evaluation continues after the packet is logged. Table 64. log statement options ┌─────────────────┬──────────────────────────┬──────────────────────────┐ │ Keyword │ Description │ Type │ ├─────────────────┼──────────────────────────┼──────────────────────────┤ │ │ │ │ │ prefix │ Log message prefix │ quoted string │ ├─────────────────┼──────────────────────────┼──────────────────────────┤ │ │ │ │ │ level │ Syslog level of logging │ string: emerg, alert, │ │ │ │ crit, err, warn │ │ │ │ [default], notice, info, │ │ │ │ debug, audit │ ├─────────────────┼──────────────────────────┼──────────────────────────┤ │ │ │ │ │ group │ NFLOG group to send │ unsigned integer (16 │ │ │ messages to │ bit) │ ├─────────────────┼──────────────────────────┼──────────────────────────┤ │ │ │ │ │ snaplen │ Length of packet payload │ unsigned integer (32 │ │ │ to include in netlink │ bit) │ │ │ message │ │ ├─────────────────┼──────────────────────────┼──────────────────────────┤ │ │ │ │ │ queue-threshold │ Number of packets to │ unsigned integer (32 │ │ │ queue inside the kernel │ bit) │ │ │ before sending them to │ │ │ │ userspace │ │ └─────────────────┴──────────────────────────┴──────────────────────────┘ Table 65. log-flags ┌──────────────┬─────────────────────────────────┐ │ Flag │ Description │ ├──────────────┼─────────────────────────────────┤ │ │ │ │ tcp sequence │ Log TCP sequence numbers. │ ├──────────────┼─────────────────────────────────┤ │ │ │ │ tcp options │ Log options from the TCP packet │ │ │ header. │ ├──────────────┼─────────────────────────────────┤ │ │ │ │ ip options │ Log options from the IP/IPv6 │ │ │ packet header. │ ├──────────────┼─────────────────────────────────┤ │ │ │ │ skuid │ Log the userid of the process │ │ │ which generated the packet. │ ├──────────────┼─────────────────────────────────┤ │ │ │ │ ether │ Decode MAC addresses and │ │ │ protocol. │ ├──────────────┼─────────────────────────────────┤ │ │ │ │ all │ Enable all log flags listed │ │ │ above. │ └──────────────┴─────────────────────────────────┘ Using log statement. # log the UID which generated the packet and ip options ip filter output log flags skuid flags ip options # log the tcp sequence numbers and tcp options from the TCP packet ip filter output log flags tcp sequence,options # enable all supported log flags ip6 filter output log flags all REJECT STATEMENT reject [ with REJECT_WITH ] REJECT_WITH := icmp icmp_code | icmpv6 icmpv6_code | icmpx icmpx_code | tcp reset A reject statement is used to send back an error packet in response to the matched packet otherwise it is equivalent to drop so it is a terminating statement, ending rule traversal. This statement is only valid in base chains using the input, forward or output hooks, and user-defined chains which are only called from those chains. Table 66. different ICMP reject variants are meant for use in different table families ┌─────────┬────────┬─────────────┐ │ Variant │ Family │ Type │ ├─────────┼────────┼─────────────┤ │ │ │ │ │ icmp │ ip │ icmp_code │ ├─────────┼────────┼─────────────┤ │ │ │ │ │ icmpv6 │ ip6 │ icmpv6_code │ ├─────────┼────────┼─────────────┤ │ │ │ │ │ icmpx │ inet │ icmpx_code │ └─────────┴────────┴─────────────┘ For a description of the different types and a list of supported keywords refer to DATA TYPES section above. The common default reject value is port-unreachable. Note that in bridge family, reject statement is only allowed in base chains which hook into input or prerouting. COUNTER STATEMENT A counter statement sets the hit count of packets along with the number of bytes. counter packets number bytes number counter { packets number | bytes number } CONNTRACK STATEMENT The conntrack statement can be used to set the conntrack mark and conntrack labels. ct {mark | event | label | zone} set value The ct statement sets meta data associated with a connection. The zone id has to be assigned before a conntrack lookup takes place, i.e. this has to be done in prerouting and possibly output (if locally generated packets need to be placed in a distinct zone), with a hook priority of raw (-300). Unlike iptables, where the helper assignment happens in the raw table, the helper needs to be assigned after a conntrack entry has been found, i.e. it will not work when used with hook priorities equal or before -200. Table 67. Conntrack statement types ┌─────────┬──────────────────────────┬──────────────────────┐ │ Keyword │ Description │ Value │ ├─────────┼──────────────────────────┼──────────────────────┤ │ │ │ │ │ event │ conntrack event bits │ bitmask, integer (32 │ │ │ │ bit) │ ├─────────┼──────────────────────────┼──────────────────────┤ │ │ │ │ │ helper │ name of ct helper object │ quoted string │ │ │ to assign to the │ │ │ │ connection │ │ ├─────────┼──────────────────────────┼──────────────────────┤ │ │ │ │ │ mark │ Connection tracking mark │ mark │ ├─────────┼──────────────────────────┼──────────────────────┤ │ │ │ │ │ label │ Connection tracking │ label │ │ │ label │ │ ├─────────┼──────────────────────────┼──────────────────────┤ │ │ │ │ │ zone │ conntrack zone │ integer (16 bit) │ └─────────┴──────────────────────────┴──────────────────────┘ save packet nfmark in conntrack. ct mark set meta mark set zone mapped via interface. table inet raw { chain prerouting { type filter hook prerouting priority raw; ct zone set iif map { "eth1" : 1, "veth1" : 2 } } chain output { type filter hook output priority raw; ct zone set oif map { "eth1" : 1, "veth1" : 2 } } } restrict events reported by ctnetlink. ct event set new,related,destroy NOTRACK STATEMENT The notrack statement allows one to disable connection tracking for certain packets. notrack Note that for this statement to be effective, it has to be applied to packets before a conntrack lookup happens. Therefore, it needs to sit in a chain with either prerouting or output hook and a hook priority of -300 (raw) or less. See SYNPROXY STATEMENT for an example usage. META STATEMENT A meta statement sets the value of a meta expression. The existing meta fields are: priority, mark, pkttype, nftrace. meta {mark | priority | pkttype | nftrace | broute} set value A meta statement sets meta data associated with a packet. Table 68. Meta statement types ┌──────────┬────────────────────────┬───────────┐ │ Keyword │ Description │ Value │ ├──────────┼────────────────────────┼───────────┤ │ │ │ │ │ priority │ TC packet priority │ tc_handle │ ├──────────┼────────────────────────┼───────────┤ │ │ │ │ │ mark │ Packet mark │ mark │ ├──────────┼────────────────────────┼───────────┤ │ │ │ │ │ pkttype │ packet type │ pkt_type │ ├──────────┼────────────────────────┼───────────┤ │ │ │ │ │ nftrace │ ruleset packet tracing │ 0, 1 │ │ │ on/off. Use monitor │ │ │ │ trace command to watch │ │ │ │ traces │ │ ├──────────┼────────────────────────┼───────────┤ │ │ │ │ │ broute │ broute on/off. packets │ 0, 1 │ │ │ are routed instead of │ │ │ │ being bridged │ │ └──────────┴────────────────────────┴───────────┘ LIMIT STATEMENT limit rate [over] packet_number / TIME_UNIT [burst packet_number packets] limit rate [over] byte_number BYTE_UNIT / TIME_UNIT [burst byte_number BYTE_UNIT] TIME_UNIT := second | minute | hour | day BYTE_UNIT := bytes | kbytes | mbytes A limit statement matches at a limited rate using a token bucket filter. A rule using this statement will match until this limit is reached. It can be used in combination with the log statement to give limited logging. The optional over keyword makes it match over the specified rate. The burst value influences the bucket size, i.e. jitter tolerance. With packet-based limit, the bucket holds exactly burst packets, by default five. If you specify packet burst, it must be a non-zero value. With byte-based limit, the bucket’s minimum size is the given rate’s byte value and the burst value adds to that, by default zero bytes. Table 69. limit statement values ┌───────────────┬───────────────────┬──────────────────────┐ │ Value │ Description │ Type │ ├───────────────┼───────────────────┼──────────────────────┤ │ │ │ │ │ packet_number │ Number of packets │ unsigned integer (32 │ │ │ │ bit) │ ├───────────────┼───────────────────┼──────────────────────┤ │ │ │ │ │ byte_number │ Number of bytes │ unsigned integer (32 │ │ │ │ bit) │ └───────────────┴───────────────────┴──────────────────────┘ NAT STATEMENTS snat [[ip | ip6] [ prefix ] to] ADDR_SPEC [:PORT_SPEC] [FLAGS] dnat [[ip | ip6] [ prefix ] to] ADDR_SPEC [:PORT_SPEC] [FLAGS] masquerade [to :PORT_SPEC] [FLAGS] redirect [to :PORT_SPEC] [FLAGS] ADDR_SPEC := address | address - address PORT_SPEC := port | port - port FLAGS := FLAG [, FLAGS] FLAG := persistent | random | fully-random The nat statements are only valid from nat chain types. The snat and masquerade statements specify that the source address of the packet should be modified. While snat is only valid in the postrouting and input chains, masquerade makes sense only in postrouting. The dnat and redirect statements are only valid in the prerouting and output chains, they specify that the destination address of the packet should be modified. You can use non-base chains which are called from base chains of nat chain type too. All future packets in this connection will also be mangled, and rules should cease being examined. The masquerade statement is a special form of snat which always uses the outgoing interface’s IP address to translate to. It is particularly useful on gateways with dynamic (public) IP addresses. The redirect statement is a special form of dnat which always translates the destination address to the local host’s one. It comes in handy if one only wants to alter the destination port of incoming traffic on different interfaces. When used in the inet family (available with kernel 5.2), the dnat and snat statements require the use of the ip and ip6 keyword in case an address is provided, see the examples below. Before kernel 4.18 nat statements require both prerouting and postrouting base chains to be present since otherwise packets on the return path won’t be seen by netfilter and therefore no reverse translation will take place. The optional prefix keyword allows to map to map n source addresses to n destination addresses. See Advanced NAT examples below. Table 70. NAT statement values ┌────────────┬──────────────────────────┬─────────────────────────┐ │ Expression │ Description │ Type │ ├────────────┼──────────────────────────┼─────────────────────────┤ │ │ │ │ │ address │ Specifies that the │ ipv4_addr, ipv6_addr, │ │ │ source/destination │ e.g. abcd::1234, or you │ │ │ address of the packet │ can use a mapping, e.g. │ │ │ should be modified. You │ meta mark map { 10 : │ │ │ may specify a mapping to │ 192.168.1.2, 20 : │ │ │ relate a list of tuples │ 192.168.1.3 } │ │ │ composed of arbitrary │ │ │ │ expression key with │ │ │ │ address value. │ │ ├────────────┼──────────────────────────┼─────────────────────────┤ │ │ │ │ │ port │ Specifies that the │ port number (16 bit) │ │ │ source/destination port │ │ │ │ of the packet should be │ │ │ │ modified. │ │ └────────────┴──────────────────────────┴─────────────────────────┘ Table 71. NAT statement flags ┌──────────────┬──────────────────────────────────┐ │ Flag │ Description │ ├──────────────┼──────────────────────────────────┤ │ │ │ │ persistent │ Gives a client the same │ │ │ source-/destination-address for │ │ │ each connection. │ ├──────────────┼──────────────────────────────────┤ │ │ │ │ random │ In kernel 5.0 and newer this is │ │ │ the same as fully-random. In │ │ │ earlier kernels the port mapping │ │ │ will be randomized using a │ │ │ seeded MD5 hash mix using source │ │ │ and destination address and │ │ │ destination port. │ ├──────────────┼──────────────────────────────────┤ │ │ │ │ fully-random │ If used then port mapping is │ │ │ generated based on a 32-bit │ │ │ pseudo-random algorithm. │ └──────────────┴──────────────────────────────────┘ Using NAT statements. # create a suitable table/chain setup for all further examples add table nat add chain nat prerouting { type nat hook prerouting priority dstnat; } add chain nat postrouting { type nat hook postrouting priority srcnat; } # translate source addresses of all packets leaving via eth0 to address 1.2.3.4 add rule nat postrouting oif eth0 snat to 1.2.3.4 # redirect all traffic entering via eth0 to destination address 192.168.1.120 add rule nat prerouting iif eth0 dnat to 192.168.1.120 # translate source addresses of all packets leaving via eth0 to whatever # locally generated packets would use as source to reach the same destination add rule nat postrouting oif eth0 masquerade # redirect incoming TCP traffic for port 22 to port 2222 add rule nat prerouting tcp dport 22 redirect to :2222 # inet family: # handle ip dnat: add rule inet nat prerouting dnat ip to 10.0.2.99 # handle ip6 dnat: add rule inet nat prerouting dnat ip6 to fe80::dead # this masquerades both ipv4 and ipv6: add rule inet nat postrouting meta oif ppp0 masquerade Advanced NAT examples. # map prefixes in one network to that of another, e.g. 10.141.11.4 is mangled to 192.168.2.4, # 10.141.11.5 is mangled to 192.168.2.5 and so on. add rule nat postrouting snat ip prefix to ip saddr map { 10.141.11.0/24 : 192.168.2.0/24 } # map a source address, source port combination to a pool of destination addresses and ports: add rule nat postrouting dnat to ip saddr . tcp dport map { 192.168.1.2 . 80 : 10.141.10.2-10.141.10.5 . 8888-8999 } # The above example generates the following NAT expression: # # [ nat dnat ip addr_min reg 1 addr_max reg 10 proto_min reg 9 proto_max reg 11 ] # # which expects to obtain the following tuple: # IP address (min), source port (min), IP address (max), source port (max) # to be obtained from the map. The given addresses and ports are inclusive. # This also works with named maps and in combination with both concatenations and ranges: table ip nat { map ipportmap { typeof ip saddr : interval ip daddr . tcp dport flags interval elements = { 192.168.1.2 : 10.141.10.1-10.141.10.3 . 8888-8999, 192.168.2.0/24 : 10.141.11.5-10.141.11.20 . 8888-8999 } } chain prerouting { type nat hook prerouting priority dstnat; policy accept; ip protocol tcp dnat ip to ip saddr map @ipportmap } } @ipportmap maps network prefixes to a range of hosts and ports. The new destination is taken from the range provided by the map element. Same for the destination port. Note the use of the "interval" keyword in the typeof description. This is required so nftables knows that it has to ask for twice the amount of storage for each key-value pair in the map. ": ipv4_addr . inet_service" would allow associating one address and one port with each key. But for this case, for each key, two addresses and two ports (The minimum and maximum values for both) have to be stored. TPROXY STATEMENT Tproxy redirects the packet to a local socket without changing the packet header in any way. If any of the arguments is missing the data of the incoming packet is used as parameter. Tproxy matching requires another rule that ensures the presence of transport protocol header is specified. tproxy to address:port tproxy to {address | :port} This syntax can be used in ip/ip6 tables where network layer protocol is obvious. Either IP address or port can be specified, but at least one of them is necessary. tproxy {ip | ip6} to address[:port] tproxy to :port This syntax can be used in inet tables. The ip/ip6 parameter defines the family the rule will match. The address parameter must be of this family. When only port is defined, the address family should not be specified. In this case the rule will match for both families. Table 72. tproxy attributes ┌─────────┬─────────────────────────────────┐ │ Name │ Description │ ├─────────┼─────────────────────────────────┤ │ │ │ │ address │ IP address the listening socket │ │ │ with IP_TRANSPARENT option is │ │ │ bound to. │ ├─────────┼─────────────────────────────────┤ │ │ │ │ port │ Port the listening socket with │ │ │ IP_TRANSPARENT option is bound │ │ │ to. │ └─────────┴─────────────────────────────────┘ Example ruleset for tproxy statement. table ip x { chain y { type filter hook prerouting priority mangle; policy accept; tcp dport ntp tproxy to 1.1.1.1 udp dport ssh tproxy to :2222 } } table ip6 x { chain y { type filter hook prerouting priority mangle; policy accept; tcp dport ntp tproxy to [dead::beef] udp dport ssh tproxy to :2222 } } table inet x { chain y { type filter hook prerouting priority mangle; policy accept; tcp dport 321 tproxy to :ssh tcp dport 99 tproxy ip to 1.1.1.1:999 udp dport 155 tproxy ip6 to [dead::beef]:smux } } SYNPROXY STATEMENT This statement will process TCP three-way-handshake parallel in netfilter context to protect either local or backend system. This statement requires connection tracking because sequence numbers need to be translated. synproxy [mss mss_value] [wscale wscale_value] [SYNPROXY_FLAGS] Table 73. synproxy statement attributes ┌────────┬─────────────────────────────────┐ │ Name │ Description │ ├────────┼─────────────────────────────────┤ │ │ │ │ mss │ Maximum segment size announced │ │ │ to clients. This must match the │ │ │ backend. │ ├────────┼─────────────────────────────────┤ │ │ │ │ wscale │ Window scale announced to │ │ │ clients. This must match the │ │ │ backend. │ └────────┴─────────────────────────────────┘ Table 74. synproxy statement flags ┌───────────┬──────────────────────────────────┐ │ Flag │ Description │ ├───────────┼──────────────────────────────────┤ │ │ │ │ sack-perm │ Pass client selective │ │ │ acknowledgement option to │ │ │ backend (will be disabled if not │ │ │ present). │ ├───────────┼──────────────────────────────────┤ │ │ │ │ timestamp │ Pass client timestamp option to │ │ │ backend (will be disabled if not │ │ │ present, also needed for │ │ │ selective acknowledgement and │ │ │ window scaling). │ └───────────┴──────────────────────────────────┘ Example ruleset for synproxy statement. Determine tcp options used by backend, from an external system tcpdump -pni eth0 -c 1 'tcp[tcpflags] == (tcp-syn|tcp-ack)' port 80 & telnet 192.0.2.42 80 18:57:24.693307 IP 192.0.2.42.80 > 192.0.2.43.48757: Flags [S.], seq 360414582, ack 788841994, win 14480, options [mss 1460,sackOK, TS val 1409056151 ecr 9690221, nop,wscale 9], length 0 Switch tcp_loose mode off, so conntrack will mark out-of-flow packets as state INVALID. echo 0 > /proc/sys/net/netfilter/nf_conntrack_tcp_loose Make SYN packets untracked. table ip x { chain y { type filter hook prerouting priority raw; policy accept; tcp flags syn notrack } } Catch UNTRACKED (SYN packets) and INVALID (3WHS ACK packets) states and send them to SYNPROXY. This rule will respond to SYN packets with SYN+ACK syncookies, create ESTABLISHED for valid client response (3WHS ACK packets) and drop incorrect cookies. Flags combinations not expected during 3WHS will not match and continue (e.g. SYN+FIN, SYN+ACK). Finally, drop invalid packets, this will be out-of-flow packets that were not matched by SYNPROXY. table ip x { chain z { type filter hook input priority filter; policy accept; ct state invalid, untracked synproxy mss 1460 wscale 9 timestamp sack-perm ct state invalid drop } } FLOW STATEMENT A flow statement allows us to select what flows you want to accelerate forwarding through layer 3 network stack bypass. You have to specify the flowtable name where you want to offload this flow. flow add @flowtable QUEUE STATEMENT This statement passes the packet to userspace using the nfnetlink_queue handler. The packet is put into the queue identified by its 16-bit queue number. Userspace can inspect and modify the packet if desired. Userspace must then drop or re-inject the packet into the kernel. See libnetfilter_queue documentation for details. queue [flags QUEUE_FLAGS] [to queue_number] queue [flags QUEUE_FLAGS] [to queue_number_from - queue_number_to] queue [flags QUEUE_FLAGS] [to QUEUE_EXPRESSION ] QUEUE_FLAGS := QUEUE_FLAG [, QUEUE_FLAGS] QUEUE_FLAG := bypass | fanout QUEUE_EXPRESSION := numgen | hash | symhash | MAP STATEMENT QUEUE_EXPRESSION can be used to compute a queue number at run-time with the hash or numgen expressions. It also allows one to use the map statement to assign fixed queue numbers based on external inputs such as the source ip address or interface names. Table 75. queue statement values ┌───────────────────┬─────────────────────────┬──────────────────────┐ │ Value │ Description │ Type │ ├───────────────────┼─────────────────────────┼──────────────────────┤ │ │ │ │ │ queue_number │ Sets queue number, │ unsigned integer (16 │ │ │ default is 0. │ bit) │ ├───────────────────┼─────────────────────────┼──────────────────────┤ │ │ │ │ │ queue_number_from │ Sets initial queue in │ unsigned integer (16 │ │ │ the range, if fanout is │ bit) │ │ │ used. │ │ ├───────────────────┼─────────────────────────┼──────────────────────┤ │ │ │ │ │ queue_number_to │ Sets closing queue in │ unsigned integer (16 │ │ │ the range, if fanout is │ bit) │ │ │ used. │ │ └───────────────────┴─────────────────────────┴──────────────────────┘ Table 76. queue statement flags ┌────────┬───────────────────────────────┐ │ Flag │ Description │ ├────────┼───────────────────────────────┤ │ │ │ │ bypass │ Let packets go through if │ │ │ userspace application cannot │ │ │ back off. Before using this │ │ │ flag, read libnetfilter_queue │ │ │ documentation for performance │ │ │ tuning recommendations. │ ├────────┼───────────────────────────────┤ │ │ │ │ fanout │ Distribute packets between │ │ │ several queues. │ └────────┴───────────────────────────────┘ DUP STATEMENT The dup statement is used to duplicate a packet and send the copy to a different destination. dup to device dup to address device device Table 77. Dup statement values ┌────────────┬─────────────────────────┬──────────────────────────┐ │ Expression │ Description │ Type │ ├────────────┼─────────────────────────┼──────────────────────────┤ │ │ │ │ │ address │ Specifies that the copy │ ipv4_addr, ipv6_addr, │ │ │ of the packet should be │ e.g. abcd::1234, or you │ │ │ sent to a new gateway. │ can use a mapping, e.g. │ │ │ │ ip saddr map { │ │ │ │ 192.168.1.2 : 10.1.1.1 } │ ├────────────┼─────────────────────────┼──────────────────────────┤ │ │ │ │ │ device │ Specifies that the copy │ string │ │ │ should be transmitted │ │ │ │ via device. │ │ └────────────┴─────────────────────────┴──────────────────────────┘ Using the dup statement. # send to machine with ip address 10.2.3.4 on eth0 ip filter forward dup to 10.2.3.4 device "eth0" # copy raw frame to another interface netdev ingress dup to "eth0" dup to "eth0" # combine with map dst addr to gateways dup to ip daddr map { 192.168.7.1 : "eth0", 192.168.7.2 : "eth1" } FWD STATEMENT The fwd statement is used to redirect a raw packet to another interface. It is only available in the netdev family ingress and egress hooks. It is similar to the dup statement except that no copy is made. You can also specify the address of the next hop and the device to forward the packet to. This updates the source and destination MAC address of the packet by transmitting it through the neighboring layer. This also decrements the ttl field of the IP packet. This provides a way to effectively bypass the classical forwarding path, thus skipping the fib (forwarding information base) lookup. fwd to device fwd [ip | ip6] to address device device Using the fwd statement. # redirect raw packet to device netdev ingress fwd to "eth0" # forward packet to next hop 192.168.200.1 via eth0 device netdev ingress ether saddr set fwd ip to 192.168.200.1 device "eth0" SET STATEMENT The set statement is used to dynamically add or update elements in a set from the packet path. The set setname must already exist in the given table and must have been created with one or both of the dynamic and the timeout flags. The dynamic flag is required if the set statement expression includes a stateful object. The timeout flag is implied if the set is created with a timeout, and is required if the set statement updates elements, rather than adding them. Furthermore, these sets should specify both a maximum set size (to prevent memory exhaustion), and their elements should have a timeout (so their number will not grow indefinitely) either from the set definition or from the statement that adds or updates them. The set statement can be used to e.g. create dynamic blacklists. Dynamic updates are also supported with maps. In this case, the add or update rule needs to provide both the key and the data element (value), separated via :. {add | update} @setname { expression [timeout timeout] [comment string] } Example for simple blacklist. # declare a set, bound to table "filter", in family "ip". # Timeout and size are mandatory because we will add elements from packet path. # Entries will timeout after one minute, after which they might be # re-added if limit condition persists. nft add set ip filter blackhole \ "{ type ipv4_addr; flags dynamic; timeout 1m; size 65536; }" # declare a set to store the limit per saddr. # This must be separate from blackhole since the timeout is different nft add set ip filter flood \ "{ type ipv4_addr; flags dynamic; timeout 10s; size 128000; }" # whitelist internal interface. nft add rule ip filter input meta iifname "internal" accept # drop packets coming from blacklisted ip addresses. nft add rule ip filter input ip saddr @blackhole counter drop # add source ip addresses to the blacklist if more than 10 tcp connection # requests occurred per second and ip address. nft add rule ip filter input tcp flags syn tcp dport ssh \ add @flood { ip saddr limit rate over 10/second } \ add @blackhole { ip saddr } \ drop # inspect state of the sets. nft list set ip filter flood nft list set ip filter blackhole # manually add two addresses to the blackhole. nft add element filter blackhole { 10.2.3.4, 10.23.1.42 } MAP STATEMENT The map statement is used to lookup data based on some specific input key. expression map { MAP_ELEMENTS } MAP_ELEMENTS := MAP_ELEMENT [, MAP_ELEMENTS] MAP_ELEMENT := key : value The key is a value returned by expression. Using the map statement. # select DNAT target based on TCP dport: # connections to port 80 are redirected to 192.168.1.100, # connections to port 8888 are redirected to 192.168.1.101 nft add rule ip nat prerouting dnat tcp dport map { 80 : 192.168.1.100, 8888 : 192.168.1.101 } # source address based SNAT: # packets from net 192.168.1.0/24 will appear as originating from 10.0.0.1, # packets from net 192.168.2.0/24 will appear as originating from 10.0.0.2 nft add rule ip nat postrouting snat to ip saddr map { 192.168.1.0/24 : 10.0.0.1, 192.168.2.0/24 : 10.0.0.2 } VMAP STATEMENT The verdict map (vmap) statement works analogous to the map statement, but contains verdicts as values. expression vmap { VMAP_ELEMENTS } VMAP_ELEMENTS := VMAP_ELEMENT [, VMAP_ELEMENTS] VMAP_ELEMENT := key : verdict Using the vmap statement. # jump to different chains depending on layer 4 protocol type: nft add rule ip filter input ip protocol vmap { tcp : jump tcp-chain, udp : jump udp-chain , icmp : jump icmp-chain } XT STATEMENT This represents an xt statement from xtables compat interface. It is a fallback if translation is not available or not complete. xt TYPE NAME TYPE := match | target | watcher Seeing this means the ruleset (or parts of it) were created by iptables-nft and one should use that to manage it. BEWARE: nftables won’t restore these statements. ADDITIONAL COMMANDS These are some additional commands included in nft. MONITOR The monitor command allows you to listen to Netlink events produced by the nf_tables subsystem. These are either related to creation and deletion of objects or to packets for which meta nftrace was enabled. When they occur, nft will print to stdout the monitored events in either JSON or native nft format. monitor [new | destroy] MONITOR_OBJECT monitor trace MONITOR_OBJECT := tables | chains | sets | rules | elements | ruleset To filter events related to a concrete object, use one of the keywords in MONITOR_OBJECT. To filter events related to a concrete action, use keyword new or destroy. The second form of invocation takes no further options and exclusively prints events generated for packets with nftrace enabled. Hit ^C to finish the monitor operation. Listen to all events, report in native nft format. % nft monitor Listen to deleted rules, report in JSON format. % nft -j monitor destroy rules Listen to both new and destroyed chains, in native nft format. % nft monitor chains Listen to ruleset events such as table, chain, rule, set, counters and quotas, in native nft format. % nft monitor ruleset Trace incoming packets from host 10.0.0.1. % nft add rule filter input ip saddr 10.0.0.1 meta nftrace set 1 % nft monitor trace ERROR REPORTING When an error is detected, nft shows the line(s) containing the error, the position of the erroneous parts in the input stream and marks up the erroneous parts using carets (^). If the error results from the combination of two expressions or statements, the part imposing the constraints which are violated is marked using tildes (~). For errors returned by the kernel, nft cannot detect which parts of the input caused the error and the entire command is marked. Error caused by single incorrect expression. <cmdline>:1:19-22: Error: Interface does not exist filter output oif eth0 ^^^^ Error caused by invalid combination of two expressions. <cmdline>:1:28-36: Error: Right hand side of relational expression (==) must be constant filter output tcp dport == tcp dport ~~ ^^^^^^^^^ Error returned by the kernel. <cmdline>:0:0-23: Error: Could not process rule: Operation not permitted filter output oif wlan0 ^^^^^^^^^^^^^^^^^^^^^^^ EXIT STATUS On success, nft exits with a status of 0. Unspecified errors cause it to exit with a status of 1, memory allocation errors with a status of 2, unable to open Netlink socket with 3. SEE ALSO libnftables(3), libnftables-json(5), iptables(8), ip6tables(8), arptables(8), ebtables(8), ip(8), tc(8) There is an official wiki at: https://wiki.nftables.org AUTHORS nftables was written by Patrick McHardy and Pablo Neira Ayuso, among many other contributors from the Netfilter community. COPYRIGHT Copyright © 2008-2014 Patrick McHardy <kaber@trash.net> Copyright © 2013-2018 Pablo Neira Ayuso <pablo@netfilter.org> nftables is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License version 2 as published by the Free Software Foundation. This documentation is licensed under the terms of the Creative Commons Attribution-ShareAlike 4.0 license, CC BY-SA 4.0 http://creativecommons.org/licenses/by-sa/4.0/. 10/11/2023 NFT(8)