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 of the nftables framework for packet filtering and classification nft -nNscae -I directory -f filename -i cmd nft -h nft -v 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. 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, --reversedns Translate IP addresses to names. Usually requires network traffic for DNS lookup. -s, --stateless Omit stateful information of rules and stateful objects. -c, --check Check commands validity without actually applying the changes. -a, --handle Show object handles in output. -e, --echo When inserting items into the ruleset using add, insert or replace commands, print notifications just like nft monitor. -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. -f, --file filename Read input from filename. nft scripts must start #!/usr/sbin/nft -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. 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. You can override this behaviour either by prepending ./ to your path to force inclusion of files located in the current working directory (ie. 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 -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. 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 IPv4 ARP packets. 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 list of supported hooks is identical to IPv4/IPv6/Inet address families above. 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. list flush ruleset family export ruleset format 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. export Print the ruleset in machine readable format. The mandatory format parameter may be either xml or json. It is possible to limit list and flush to a specific address family only. For a list of valid family names, see ADDRESS FAMILIES above. Note that contrary to what one might assume, the output generated by export is not parseable by nft -f. Instead, the output of list command serves well for that purpose. add create table family table flags flags delete list flush table family table delete 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. Flag Description dormant table is not evalauted any more (base chains are unregistered) # 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 0; } # 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. list List all chains and rules of the specified table. flush Flush all chains and rules of the specified table. add create chain family table chain type type hook hook device device priority priority ; policy policy ; delete list flush chain family table chain delete 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. 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. Type Families Hooks Description filter all all Standard chain type to use in doubt. nat ip, ip6 prerouting, input, output, postrouting Chains of this type perform Network 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 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 two further quirks worth noticing: netdev family supports merely a single combination, namely filter type and ingress hook. Base chains in this family also require the device parameter to be present since they exist per incoming interface only. arp family supports only input and output hooks, both in chains of type filter. The priority parameter accepts a signed integer value which specifies the order in which chains with same hook value are traversed. The ordering is ascending, i.e. lower priority values have precedence over higher ones. Base chains also allow 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. add insert rule family table chain position position statement... replace rule family table chain handle handle statement... delete rule family table chain handle handle Rules are added to chain 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. 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. replace Similar to the add command, but the rule replaces the specified rule. delete Delete the specified rule. 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 # nft -a list ruleset table inet filter { chain input { type filter hook input priority 0; 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 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 anoymous set is declared it cannot be changed anymore except by removing/altering the rule that uses the anonymous set. 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. nft add rule filter input ip saddr @allowed_hosts tcp dport @allowed_ports accept The sets allowed_hosts and allowed_portsneed to be created first. The next section describes nft set syntax in more detail. add set family table set { type type ; flags flags ; timeout timeout ; gc-interval gc-interval ; elements = { element[,...] } ; size size ; policy policy ; auto-merge auto-merge ; } delete list flush set family table set delete set family table handle handle add delete element family table set { element[,...] } Sets are elements containers of an user-defined data type, they are uniquely identified by an user-defined name and attached to tables. add Add a new set in the specified table. delete Delete the specified set. list Display the elements in the specified set. flush Remove all elements from the specified set. add element Comma-separated list of elements to add into the specified set. delete element Comma-separated list of elements to delete from the specified set. Keyword Description Type type data type of set elements string: ipv4_addr, ipv6_addr, ether_addr, inet_proto, inet_service, mark flags set flags string: constant, interval, timeout timeout time an element stays in the set, mandatory if set is added to from the packet path (ruleset). string, decimal followed by unit. Units are: d, h, m, s gc-interval garbage collection interval, only available when timeout or flag timeout are active string, decimal followed by unit. Units are: d, h, m, s elements elements contained by the set set data type size maximun number of elements in the set, mandatory if set is added to from the packet path (ruleset). unsigned integer (64 bit) policy set policy string: performance [default], memory auto-merge automatic merge of adjacent/overlapping set elements (only for interval sets) add map family table map { type type flags flags ; elements = { element[,...] } ; size size ; policy policy ; } delete list flush map family table map add delete element family table map { elements = { element[,...] } ; } Maps store data based on some specific key used as input, they are uniquely identified by an user-defined name and attached to tables. add Add a new map in the specified table. delete Delete the specified map. list Display the elements in the specified map. flush Remove all elements from the specified map. add element Comma-separated list of elements to add into the specified map. delete element Comma-separated list of element keys to delete from the specified map. Keyword Description Type type data type of map elements string ':' string: ipv4_addr, ipv6_addr, ether_addr, inet_proto, inet_service, mark, counter, quota. Counter and quota can't be used as keys flags map flags string: constant, interval elements elements contained by the map map data type size maximun number of elements in the map unsigned integer (64 bit) policy map policy string: performance [default], memory add create flowtable family table flowtable hook hook priority priority ; devices = { device[,...] } ; delete list flowtable family table flowtable 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 what flows you want to offload through the flow offload expression from the forward chain. Flowtables are identified by their address family and their name. The address family must be one of ip ip6 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. add Add a new flowtable for the given family with the given name. delete Delete the specified flowtable. list List all flowtables. add delete list reset type family table object delete type family table handle handle Stateful objects are attached to tables and are identified by an 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. list Display stateful information the object holds. reset List-and-reset stateful object. ct helper helper { type type protocol protocol ; l3proto family ; } 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. Keyword Description Type type name of helper type quoted string (e.g. "ftp") protocol layer 4 protocol of the helper string (e.g. tcp) l3proto layer 3 protocol of the helper address family (e.g. ip) 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 0; tcp dport 21 ct helper set "ftp-standard" } } counter packets bytes Keyword Description Type packets initial count of packets unsigned integer (64 bit) bytes initial count of bytes unsigned integer (64 bit) quota over until used Keyword Description Type quota quota limit, used as the quota name Two arguments, unsigned interger (64 bit) and string: bytes, kbytes, mbytes. "over" and "until" go before these arguments used initial value of used quota Two arguments, unsigned interger (64 bit) and string: bytes, kbytes, mbytes 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. 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. # abbreviated loopback address filter output ip6 daddr ::1 # without [] the port number (22) would be parsed as part of ipv6 address ip6 nat prerouting tcp dport 2222 dnat to [1ce::d0]:22 Name Keyword Size Base type Boolean boolean 1 bit integer The boolean type is a syntactical helper type in user space. It's 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). The following keywords will automatically resolve into a boolean type with given value: Keyword Value exists 1 missing 0 The following expressions support a boolean comparison: Expression Behaviour fib Check route existence. exthdr Check IPv6 extension header existence. tcp option Check TCP option header existence. # 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 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. The following 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 # match ping packets filter output icmp type { echo-request, echo-reply } 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. The following keywords may be used when specifying the ICMP code: Keyword Value net-unreachable 0 host-unreachable 1 prot-unreachable 2 port-unreachable 3 net-prohibited 9 host-prohibited 10 admin-prohibited 13 Name Keyword Size Base type ICMPv6 Type icmpv6_type 8 bit integer The ICMPv6 Type type is used to conveniently specify the ICMPv6 header's type field. The following 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 # match ICMPv6 ping packets filter output icmpv6 type { echo-request, echo-reply } 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. The following 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 Name Keyword Size Base type ICMPvX Code icmpx_code 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. The following keywords may be used when specifying the ICMPvX code: Keyword Value no-route 0 port-unreachable 1 host-unreachable 2 admin-prohibited 3 This is an 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 bits ct_event 4 byte bitmask conntrack label ct_label 128 bit bitmask For each of the types above, keywords are available for convenience: Keyword Value invalid 1 established 2 related 4 new 8 untracked 64 Keyword Value original 0 reply 1 Keyword Value expected 1 seen-reply 2 assured 4 confirmed 8 snat 16 dnat 32 dying 512 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. 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 secpath 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. Keyword Description Type length Length of the packet in bytes integer (32 bit) nfproto real hook protocol family, useful only in inet table integer (32 bit) l4proto layer 4 protocol, skips ipv6 extension headers integer (8 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 ifname iiftype Input interface type iface_type oif Output interface index iface_index oifname Output interface name ifname 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 ifname obriport Output bridge interface name ifname 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) secpath boolean boolean (1 bit) 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 # packed was subject to ipsec processing raw prerouting meta secpath exists accept 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 missing drop # drop packets to address not configured on ininterface 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 } 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 mtu TCP maximum segment size of route integer (16 bit) 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 output rt ip nexthop 192.168.0.1 inet filter output rt ip6 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 icmp ICMP header field 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 request/response integer (16 bit) sequence sequence number of echo request/response integer (16 bit) gateway gateway of redirects integer (32 bit) mtu MTU of path MTU discovery integer (16 bit) ip6 IPv6 header field 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. 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 ip6 nexthdr ipv6-frag counter icmpv6 ICMPv6 header field 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 request/response integer (16 bit) sequence sequence number of echo request/response integer (16 bit) max-delay maximum response delay of MLD queries integer (16 bit) 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 Verification 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) @ base,offset,length The raw payload expression instructs to load lengthbits starting at offsetbits. Bit 0 refers the 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 my using meta l4proto 5 before the raw expression. Base Description ll Link layer, for example the ethernet header nh Network header, for example IPv4 or IPv6 th Transport Header, for example TCP inet filter input meta l4proto {tcp, udp} @th,16,16 { dns, http } 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 refer to data from variable-sized protocol headers, such as IPv6 extension headers and TCPs options. nftables currently supports matching (finding) a given ipv6 extension header or TCP 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 noop maxseg window sack-permitted sack sack0 sack1 sack2 sack3 timestamp tcp_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 noop maxseg window sack-permitted sack sack0 sack1 sack2 sack3 timestamp Keyword Description hbh Hop by Hop rt Routing Header frag Fragmentation header dst dst options mh Mobility Header srh Segment Routing Header Keyword Description TCP option fields eol End of option list kind noop 1 Byte TCP No-op options kind maxseg TCP Maximum Segment Size kind, length, size window TCP Window Scaling kind, length, count sack-permitted TCP SACK permitted kind, length sack TCP Selective Acknowledgement (alias of block 0) kind, length, left, right sack0 TCP Selective Acknowledgement (block 0) kind, length, left, right sack1 TCP Selective Acknowledgement (block 1) kind, length, left, right sack2 TCP Selective Acknowledgement (block 2) kind, length, left, right sack3 TCP Selective Acknowledgement (block 3) kind, length, left, right timestamp TCP Timestamps kind, length, tsval, tsecr filter input tcp option sack-permitted kind 1 counter ip6 filter input frag more-fragments 1 counter 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 l3proto protocol bytes packets avgpkt zone ct original reply l3proto protocol proto-src proto-dst bytes packets avgpkt zone ct original reply ip ip6 saddr daddr 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) zone conntrack zone integer (16 bit) A description of conntrack-specific types listed above can be found sub-section CONNTRACK TYPES above. 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 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 TCPMSS. 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 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 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. The different ICMP reject variants are meant for use in different table families: Variant Family Type icmp ip icmp_code icmp6 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. 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 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 -300. Keyword Description Value event conntrack event bits bitmask, integer (32 bit) helper name of ct helper object to assign to the connection quoted string mark Connection tracking mark mark label Connection tracking label label zone conntrack zone integer (16 bit) ct mark set meta mark table inet raw { chain prerouting { type filter hook prerouting priority -300; ct zone set iif map { "eth1" : 1, "veth1" : 2 } } chain output { type filter hook output priority -300; ct zone set oif map { "eth1" : 1, "veth1" : 2 } } } ct event set new,related,destroy 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 masquerade to :port persistent, random, fully-random masquerade to :port - port persistent, random, fully-random redirect to :port persistent, random, fully-random redirect to :port - port 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. Note that all 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. 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. # create a suitable table/chain setup for all further examples add table nat add chain nat prerouting { type nat hook prerouting priority 0; } add chain nat postrouting { type nat hook postrouting priority 100; } # 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 A flow offload 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 offload @flowtable 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. 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 Expression Description Type address Specifies that the copy of the packet should be sent to a new gateway. ipv4_addr, ipv6_addr, eg. abcd::1234, or you can use a mapping, eg. ip saddr map { 192.168.1.2 : 10.1.1.1 } device Specifies that the copy should be transmitted via device. string # 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 netdetv 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" } The fwd statement is used to redirect a raw packet to another interface. Its is only available in the netdev family ingress hook. It is similar to the dup statement except that no copy is made. fwd to device 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. Furhermore, any set that will be dynamically updated from the nftables ruleset must specify both a maximum set size (to prevent memory exhaustion) and a timeout (so that number of entries in set will not grow indefinitely). The set statement can be used to e.g. create dynamic blacklists. add update @setname { expression timeout timeout comment string } # declare a set, bound to table "filter", in family "ip". Timeout and size are mandatory because we will add elements from packet path. nft add set ip filter blackhole "{ type ipv4_addr; flags timeout; size 65536; }" # 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 backlist if more than 10 tcp connection requests occured per second and ip address. # entries will timeout after one minute, after which they might be re-added if limit condition persists. nft add rule ip filter input tcp flags syn tcp dport ssh meter flood { ip saddr timeout 10s limit rate over 10/second} add @blackhole { ip saddr timeout 1m } drop # inspect state of the rate limit meter: nft list meter ip filter flood # inspect content of blackhole: nft list set ip filter blackhole # manually add two addresses to the set: nft add element filter blackhole { 10.2.3.4, 10.23.1.42 } These are some additional commands included in nft. 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 occur, 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', 'ruleset'. 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 % nft monitor ruleset 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: https://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.