Patrick McHardy kaber@trash.net 2008-2014 Patrick McHardy Pablo Neira Neira Ayuso pablo@netfilter.org 2013-2016 Pablo Neira Ayuso nft 8 nft Administration tool for packet filtering and classification nft -n | --numeric [-I | --includepath] directory [-f | --file] filename [-i | --interactive] cmd nft -h | --help -v | --version nft is used to set up, maintain and inspect packet filtering and classification rules in the Linux kernel. For a full summary of options, run nft --help. -h, --help Show help message and all options. -v, --version Show version. -n, --numeric Show data numerically. When used once (the default behaviour), skip lookup of addresses to symbolic names. Use twice to also show Internet services (port numbers) numerically. Use three times to also show protocols and UIDs/GIDs numerically. -N Translate IP addresses to names. Usually requires network traffic for DNS lookup. -a, --handle Show rule handles in output. -I, --includepath directory Add the directory directory to the list of directories to be searched for included files. -f, --file filename Read input from filename. -i, --interactive Read input from an interactive readline CLI. 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 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 "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. define variable = expr $variable Symbolic variables can be defined using the define statement. Variable references are expressions and can be used initialize other variables. The scope of a definition is the current block and all blocks contained within. define int_if1 = eth0 define int_if2 = eth1 define int_ifs = { $int_if1, $int_if2 } filter input iif $int_ifs accept 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 packets vi bridge Bridge address family, handling packets which traverse a bridge device. netdev Netdev address family, handling packets from ingress. 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. 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. 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. The ARP address family handles ARP packets received and sent by the system. It is commonly used to mangle ARP packets for clustering. 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. The bridge address family handles ethernet packets traversing bridge devices. The Netdev address family handles packets from ingress. Hook Description ingress All packets entering the system are processed by this hook. It is invoked before layer 3 protocol handlers and it can be used for early filtering and policing. add delete list flush table family table Tables are containers for chains and sets. 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. When no address family is specified, ip is used by default. add Add a new table for the given family with the given name. delete Delete the specified table. list List all chains and rules of the specified table. flush Flush all chains and rules of the specified table. add chain family table chain hook priority policy device add create delete list flush chain family table chain 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 Simlar 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. rename Rename the specified chain. list List all rules of the specified chain. flush Flush all rules of the specified chain. add insert rule family table chain position position statement delete rule family table chain handle handle Rules are constructed from two kinds of components according to a set of grammatical rules: expressions and statements. add Add a new rule described by the list of statements. The rule is appended to the given chain unless a position is specified, in which case the rule is appended to the rule given by the position. insert Similar to the add command, but the rule is prepended to the beginning of the chain or before the rule at the given position. delete Delete the specified rule. 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 expression The describe command shows information about the type of an expression and its data type. $ nft describe tcp flags payload expression, datatype tcp_flag (TCP flag) (basetype bitmask, integer), 8 bits pre-defined symbolic constants: fin 0x01 syn 0x02 rst 0x04 psh 0x08 ack 0x10 urg 0x20 ecn 0x40 cwr 0x80 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. 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. Name Keyword Size Base type Integer integer variable - The integer type is used for numeric values. It may be specified as decimal, hexadecimal or octal number. The integer type doesn't have a fixed size, its size is determined by the expression for which it is used. Name Keyword Size Base type Bitmask bitmask variable integer The bitmask type (bitmask) is used for bitmasks. Name Keyword Size Base type String string variable - The string type is used to 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. # Interface name filter input iifname eth0 # Weird interface name filter input iifname "(eth0)" 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 (:). # Ethernet destination MAC address filter input ether daddr 20:c9:d0:43:12:d9 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. # dotted decimal notation filter output ip daddr 127.0.0.1 # host name filter output ip daddr localhost Name Keyword Size Base type IPv6 address ipv6_addr 128 bit integer The IPv6 address type is used for IPv6 addresses. FIXME # abbreviated loopback address filter output ip6 daddr ::1 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 length nfproto l4proto protocol priority meta mark iif iifname iiftype oif oifname oiftype skuid skgid nftrace rtclassid ibriport obriport pkttype cpu iifgroup oifgroup cgroup random 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. Keyword Description Type length Length of the packet in bytes integer (32 bit) 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 string iiftype Input interface type iface_type oif Output interface index iface_index oifname Output interface name string oiftype Output interface hardware type iface_type skuid UID associated with originating socket uid skgid GID associated with originating socket gid rtclassid Routing realm realm ibriport Input bridge interface name string obriport Output bridge interface name string pkttype packet type pkt_type cpu cpu number processing the packet integer (32 bits) iifgroup incoming device group devgroup oifgroup outgoing device group devgroup cgroup control group id integer (32 bits) random pseudo-random number integer (32 bits) 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: Unicast (addressed to local host), Broadcast (to all), Multicast (to group). # qualified meta expression filter output meta oif eth0 # unqualified meta expression filter output oif eth0 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. Keyword Description Type oif Output interface index integer (32 bit) oifname Output interface name string type Address type fib_addrtype # drop packets without a reverse path filter prerouting fib saddr . iif oif eq 0 drop # drop packets to address not configured on ininterface filter input fib daddr . iif type not { 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 { backhole : drop, prohibit : jump prohibited, unreachable : drop } rt classid nexthop A routing expression refers to routing data associated with a packet. Keyword Description Type classid Routing realm realm nexthop Routing nexthop ipv4_addr/ipv6_addr Type Description realm Routing Realm (32 bit number). Can be specified numerically or as symbolic name defined in /etc/iproute2/rt_realms. # 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 meta nfproto ipv4 output rt nexthop 192.168.0.1 inet filter meta nfproto ipv6 output rt nexthop fd00::1 Payload expressions refer to data from the packet's payload. ether ethernet header field Keyword Description Type daddr Destination MAC address ether_addr saddr Source MAC address ether_addr type EtherType ether_type vlan VLAN header field Keyword Description Type id VLAN ID (VID) integer (12 bit) cfi Canonical Format Indicator integer (1 bit) pcp Priority code point integer (3 bit) type EtherType ether_type arp ARP header field 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 ip IPv4 header field Keyword Description Type version IP header version (4) integer (4 bit) hdrlength IP header length including options integer (4 bit) FIXME scaling dscp Differentiated Services Code Point dscp ecn Explicit Congestion Notification ecn 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 ip6 IPv6 header field Keyword Description Type version IP header version (6) integer (4 bit) dscp Differentiated Services Code Point dscp ecn Explicit Congestion Notification ecn 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 tcp TCP header field 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 UDP header field 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) udplite UDP-Lite header field Keyword Description Type sport Source port inet_service dport Destination port inet_service checksum Checksum integer (16 bit) sctp SCTP header field Keyword Description Type sport Source port inet_service dport Destination port inet_service vtag Verfication Tag integer (32 bit) checksum Checksum integer (32 bit) dccp DCCP header field Keyword Description Type sport Source port inet_service dport Destination port inet_service ah AH header field 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) esp ESP header field Keyword Description Type spi Security Parameter Index integer (32 bit) sequence Sequence number integer (32 bit) comp IPComp header field Keyword Description Type nexthdr Next header protocol inet_proto flags Flags bitmask cpi Compression Parameter Index integer (16 bit) IPv6 extension header expressions refer to data from an IPv6 packet's extension headers. 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. ct state direction status mark expiration helper label l3proto protocol bytes packets avgpkt ct original reply l3proto protocol saddr daddr proto-src proto-dst bytes packets avgpkt Keyword Description Type state State of the connection ct_state direction Direction of the packet relative to the connection ct_dir status Status of the connection ct_status mark Connection mark mark expiration Connection expiration time time helper Helper associated with the connection string label Connection tracking label bit or symbolic name defined in connlabel.conf in the nftables include path ct_label l3proto Layer 3 protocol of the connection nf_proto saddr Source address of the connection for the given direction ipv4_addr/ipv6_addr daddr Destination address of the connection for the given direction ipv4_addr/ipv6_addr protocol Layer 4 protocol of the connection for the given direction inet_proto proto-src Layer 4 protocol source for the given direction integer (16 bit) proto-dst Layer 4 protocol destination for the given direction integer (16 bit) packets packet count seen in the given direction or sum of original and reply integer (64 bit) bytes bytecount seen, see description for packets keyword integer (64 bit) avgpkt average bytes per packet, see description for packets keyword integer (64 bit) 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. The verdict statement alters control flow in the ruleset and issues policy decisions for packets. accept drop queue continue return jump goto chain accept Terminate ruleset evaluation and accept the packet. drop Terminate ruleset evaluation and drop the packet. queue Terminate ruleset evaluation and queue the packet to userspace. continue Continue ruleset evaluation with the next rule. FIXME 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 accept. 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 of a return verdict is issued. 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. # 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 The payload statement alters packet content. It can be used for example to set ip DSCP (differv) header field or ipv6 flow labels. # 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 ip forward ip dscp set 42 log prefix quoted_string level syslog-level flags log-flags log group nflog_group prefix quoted_string queue-threshold value snaplen size 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). If the group number is specified, the Linux kernel will pass the packet to nfnetlink_log which will multicast the packet through a netlink socket to the specified multicast group. One or more userspace processes may subscribe to the group to receive the packets, see libnetfilter_queue documentation for details. This is a non-terminating statement, so the rule evaluation continues after the packet is logged. Keyword Description Type prefix Log message prefix quoted string syslog-level Syslog level of logging string: emerg, alert, crit, err, warn [default], notice, info, debug group NFLOG group to send messages to unsigned integer (16 bit) snaplen Length of packet payload to include in netlink message unsigned integer (32 bit) queue-threshold Number of packets to queue inside the kernel before sending them to userspace unsigned integer (32 bit) 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. # 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 with icmp icmp6 icmpx type icmp_type icmp6_type icmpx_type reject with 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 the input, forward and output chains, and user-defined chains which are only called from those chains. Value Description Type icmp_type ICMP type response to be sent to the host net-unreachable, host-unreachable, prot-unreachable, port-unreachable [default], net-prohibited, host-prohibited, admin-prohibited Value Description Type icmp6_type ICMPv6 type response to be sent to the host no-route, admin-prohibited, addr-unreachable, port-unreachable [default], policy-fail, reject-route Value Description Type icmpx_type ICMPvXtype abstraction response to be sent to the host, this is a set of types that overlap in IPv4 and IPv6 to be used from the inet family. port-unreachable [default], admin-prohibited, no-route, host-unreachable A counter statement sets the hit count of packets along with the number of bytes. counter packets number bytes number The conntrack statement can be used to set the conntrack mark and conntrack labels. ct mark label set value The ct statement sets meta data associated with a connection. Keyword Description Value mark Connection tracking mark mark label Connection tracking label label ct set mark meta mark A meta statement sets the value of a meta expression. The existing meta fields are: priority, mark, pkttype, nftrace. meta mark priority pkttype nftrace set value A meta statement sets meta data associated with a packet. Keyword Description Value priority TC packet priority tc_handle mark Packet mark mark pkttype packet type pkt_type nftrace ruleset packet tracing on/off. Use monitor trace command to watch traces 0, 1 limit rate over packet_number / second minute hour day burst packet_number packets limit rate over byte_number bytes kbytes mbytes / second minute hour day week burst byte_number bytes 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 over keyword, that is optional, makes it match over the specified rate. Value Description Type packet_number Number of packets unsigned integer (32 bit) byte_number Number of bytes unsigned integer (32 bit) snat to address :port persistent, random, fully-random snat to address - address :port - port persistent, random, fully-random dnat to address :port persistent, random, fully-random dnat to address :port - port persistent, random, fully-random The nat statements are only valid from nat chain types. The snat statement is only valid in the postrouting and input hooks, it specifies that the source address of the packet should be modified. The dnat statement is only valid in the prerouting and output chains, it specifies 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. Expression Description Type address Specifies that the source/destination address of the packet should be modified. You may specify a mapping to relate a list of tuples composed of arbitrary expression key with address value. ipv4_addr, ipv6_addr, eg. abcd::1234, or you can use a mapping, eg. meta mark map { 10 : 192.168.1.2, 20 : 192.168.1.3 } port Specifies that the source/destination address of the packet should be modified. port number (16 bits) Flag Description persistent Gives a client the same source-/destination-address for each connection. random If used then port mapping will be randomized using a random 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. 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 reinject the packet into the kernel. See libnetfilter_queue documentation for details. queue num queue_number bypass queue num queue_number_from - queue_number_to bypass,fanout Value Description Type queue_number Sets queue number, default is 0. unsigned integer (16 bit) queue_number_from Sets initial queue in the range, if fanout is used. unsigned integer (16 bit) queue_number_to Sets closing queue in the range, if fanout is used. unsigned integer (16 bit) Flag Description bypass Let packets go through if userspace application cannot back off. Before using this flag, read libnetfilter_queue documentation for performance tuning recomendations. fanout Distribute packets between several queues. These are some additional commands included in nft. Export your current ruleset in XML or JSON format to stdout. Examples: % nft export xml [...] % nft export json [...] The monitor command allows you to listen to Netlink events produced by the nf_tables subsystem, related to creation and deletion of objects. When they ocurr, nft will print to stdout the monitored events in either XML, JSON or native nft format. To filter events related to a concrete object, use one of the keywords 'tables', 'chains', 'sets', 'rules', 'elements'. To filter events related to a concrete action, use keyword 'new' or 'destroy'. Hit ^C to finish the monitor operation. % nft monitor % nft monitor new tables xml % nft monitor destroy rules json % nft monitor chains 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 carrets (^). 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 can't detect which parts of the input caused the error and the entire command is marked. <cmdline>:1:19-22: Error: Interface does not exist filter output oif eth0 ^^^^ <cmdline>:1:28-36: Error: Right hand side of relational expression (==) must be constant filter output tcp dport == tcp dport ~~ ^^^^^^^^^ <cmdline>:0:0-23: Error: Could not process rule: Operation not permitted filter output oif wlan0 ^^^^^^^^^^^^^^^^^^^^^^^ 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. iptables(8) ip6tables(8) arptables(8) ebtables(8) ip(8) tc(8) There is an official wiki at: http://wiki.nftables.org nftables was written by Patrick McHardy and Pablo Neira Ayuso, among many other contributors from the Netfilter community. Copyright © 2008-2014 Patrick McHardy kaber@trash.net Copyright © 2013-2016 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 licenced under the terms of the Creative Commons Attribution-ShareAlike 4.0 license, CC BY-SA 4.0.