Quick reference-nftables in 10 minutes

Find below some basic concepts to know before using nftables.

table refers to a container of chains with no specific semantics.

chain within a table refers to a container of rules.

rule refers to an action to be configured within a chain.

nft command line

nft is the command line tool in order to interact with nftables at userspace.

Tables

family refers to a one of the following table types: ip, arp, ip6, bridge, inet, netdev. It defaults to ip.

% nft list tables [<family>]
% nft [-n] [-a] list table [<family>] <name>
% nft (add | delete | flush) table [<family>] <name>

The argument -n shows the addresses and other information that use names in numeric format. The -a argument is used to display each rule's handle (i.e., a numerical identifier).

Chains

type refers to the kind of chain to be created. Possible types are:

• filter: Supported by arp, bridge, ip, ip6 and inet table families.
• route: Mark packets (like mangle for the output hook, for other hooks use the type filter instead), supported by ip and ip6.
• nat: In order to perform Network Address Translation, supported by ip and ip6.

hook refers to an specific stage of the packet while it's being processed through the kernel. More info in Netfilter hooks.

• The hooks for ip, ip6 and inet families are: prerouting, input, forward, output, postrouting.
• The hooks for arp family are: input, output.
• The bridge family handles ethernet packets traversing bridge devices.
• The hooks for netdev are: ingress, egress.

priority refers to a number used to order the chains or to set them between some Netfilter operations. Possible values are: NF_IP_PRI_CONNTRACK_DEFRAG (-400), NF_IP_PRI_RAW (-300), NF_IP_PRI_SELINUX_FIRST (-225), NF_IP_PRI_CONNTRACK (-200), NF_IP_PRI_MANGLE (-150), NF_IP_PRI_NAT_DST (-100), NF_IP_PRI_FILTER (0), NF_IP_PRI_SECURITY (50), NF_IP_PRI_NAT_SRC (100), NF_IP_PRI_SELINUX_LAST (225), NF_IP_PRI_CONNTRACK_HELPER (300).

policy is the default verdict statement to control the flow in the base chain. Possible values are: accept (default) and drop. Warning: Setting the policy to drop discards all packets that have not been accepted by the ruleset.

% nft (add | create) chain [<family>] <table> <name> [ \{ type <type> hook <hook> [device <device>] priority <priority> \; [policy <policy> \;] \} ]
% nft (delete | list | flush) chain [<family>] <table> <name>
% nft rename chain [<family>] <table> <name> <newname>

Rules

handle is an internal number that identifies a certain rule.

% nft add rule [<family>] <table> <chain> <matches> <statements>
% nft insert rule [<family>] <table> <chain> [position <handle>] <matches> <statements>
% nft replace rule [<family>] <table> <chain> [handle <handle>] <matches> <statements>
% nft delete rule [<family>] <table> <chain> [handle <handle>]

Inserting a new rule with nft insert inserts it at the beginning of the chain, by default. However, if you specify a position handle, then the new rule is inserted just before the rule with that handle.

Matches

matches are clues used to access to certain packet information and create filters according to them.

Ip

ip match
dscp <value>		ip dscp cs1 ip dscp != cs1 ip dscp 0x38 ip dscp != 0x20 ip dscp { cs0, cs1, cs2, cs3, cs4, cs5, cs6, cs7, af11, af12, af13, af21, af22, af23, af31, af32, af33, af41, af42, af43, ef }
length <length>	Total packet length	ip length 232 ip length != 233 ip length 333-435 ip length != 333-453 ip length { 333, 553, 673, 838 }
id <id>	IP ID	ip id 22 ip id != 233 ip id 33-45 ip id != 33-45 ip id { 33, 55, 67, 88 }
frag-off <value>	Fragmentation offset	ip frag-off & 0x1fff != 0 # match fragments ip frag-off & 0x2000 != 0 # match MF flag ip frag-off & 0x4000 != 0 # match DF flag
ttl <ttl>	Time to live	ip ttl 0 ip ttl 233 ip ttl 33-55 ip ttl != 45-50 ip ttl { 43, 53, 45 } ip ttl { 33-55 }
protocol <protocol>	Upper layer protocol	ip protocol tcp ip protocol 6 ip protocol != tcp ip protocol { icmp, esp, ah, comp, udp, udplite, tcp, dccp, sctp }
checksum <checksum>	IP header checksum	ip checksum 13172 ip checksum 22 ip checksum != 233 ip checksum 33-45 ip checksum != 33-45 ip checksum { 33, 55, 67, 88 } ip checksum { 33-55 }
saddr <ip source address>	Source address	ip saddr 192.168.2.0/24 ip saddr != 192.168.2.0/24 ip saddr 192.168.3.1 ip daddr 192.168.3.100 ip saddr != 1.1.1.1 ip saddr 1.1.1.1 ip saddr & 0xff == 1 ip saddr & 0.0.0.255 < 0.0.0.127
daddr <ip destination address>	Destination address	ip daddr 192.168.0.1 ip daddr != 192.168.0.1 ip daddr 192.168.0.1-192.168.0.250 ip daddr 10.0.0.0-10.255.255.255 ip daddr 172.16.0.0-172.31.255.255 ip daddr 192.168.3.1-192.168.4.250 ip daddr != 192.168.0.1-192.168.0.250 ip daddr { 192.168.0.1-192.168.0.250 } ip daddr { 192.168.5.1, 192.168.5.2, 192.168.5.3 }
version <version>	Ip Header version	ip version 4
hdrlength <header length>	IP header length	ip hdrlength 0 ip hdrlength 15

Ip6

ip6 match
dscp <value>		ip6 dscp cs1 ip6 dscp != cs1 ip6 dscp 0x38 ip6 dscp != 0x20 ip6 dscp { cs0, cs1, cs2, cs3, cs4, cs5, cs6, cs7, af11, af12, af13, af21, af22, af23, af31, af32, af33, af41, af42, af43, ef }
flowlabel <label>	Flow label	ip6 flowlabel 22 ip6 flowlabel != 233 ip6 flowlabel { 33, 55, 67, 88 } ip6 flowlabel { 33-55 }
length <length>	Payload length	ip6 length 232 ip6 length != 233 ip6 length 333-435 ip6 length != 333-453 ip6 length { 333, 553, 673, 838 }
nexthdr <header>	Next header type (Upper layer protocol number)	ip6 nexthdr { esp, udp, ah, comp, udplite, tcp, dccp, sctp, icmpv6 } ip6 nexthdr esp ip6 nexthdr != esp ip6 nexthdr { 33-44 } ip6 nexthdr 33-44 ip6 nexthdr != 33-44
hoplimit <hoplimit>	Hop limit	ip6 hoplimit 1 ip6 hoplimit != 233 ip6 hoplimit 33-45 ip6 hoplimit != 33-45 ip6 hoplimit { 33, 55, 67, 88 } ip6 hoplimit { 33-55 }
saddr <ip source address>	Source Address	ip6 saddr 1234:1234:1234:1234:1234:1234:1234:1234 ip6 saddr ::1234:1234:1234:1234:1234:1234:1234 ip6 saddr ::/64 ip6 saddr ::1 ip6 daddr ::2
daddr <ip destination address>	Destination Address	ip6 daddr 1234:1234:1234:1234:1234:1234:1234:1234 ip6 daddr != ::1234:1234:1234:1234:1234:1234:1234-1234:1234::1234:1234:1234:1234:1234
version <version>	IP header version	ip6 version 6

Tcp

tcp match
dport <destination port>	Destination port	tcp dport 22 tcp dport != 33-45 tcp dport { 33-55 } tcp dport { telnet, http, https } tcp dport vmap { 22 : accept, 23 : drop } tcp dport vmap { 25:accept, 28:drop }
sport < source port>	Source port	tcp sport 22 tcp sport != 33-45 tcp sport { 33, 55, 67, 88 } tcp sport { 33-55 } tcp sport vmap { 25:accept, 28:drop } tcp sport 1024 tcp dport 22
sequence <value>	Sequence number	tcp sequence 22 tcp sequence != 33-45
ackseq <value>	Acknowledgement number	tcp ackseq 22 tcp ackseq != 33-45 tcp ackseq { 33, 55, 67, 88 } tcp ackseq { 33-55 }
flags <flags>	TCP flags	tcp flags { fin, syn, rst, psh, ack, urg, ecn, cwr } tcp flags cwr tcp flags != cwr
window <value>	Window	tcp window 22 tcp window != 33-45 tcp window { 33, 55, 67, 88 } tcp window { 33-55 }
checksum <checksum>	IP header checksum	tcp checksum 22 tcp checksum != 33-45 tcp checksum { 33, 55, 67, 88 } tcp checksum { 33-55 }
urgptr <pointer>	Urgent pointer	tcp urgptr 22 tcp urgptr != 33-45 tcp urgptr { 33, 55, 67, 88 }
doff <offset>	Data offset	tcp doff 8

Udp

udp match
dport <destination port>	Destination port	udp dport 22 udp dport != 33-45 udp dport { 33-55 } udp dport { telnet, http, https } udp dport vmap { 22 : accept, 23 : drop } udp dport vmap { 25:accept, 28:drop }
sport < source port>	Source port	udp sport 22 udp sport != 33-45 udp sport { 33, 55, 67, 88 } udp sport { 33-55 } udp sport vmap { 25:accept, 28:drop } udp sport 1024 udp dport 22
length <length>	Total packet length	udp length 6666 udp length != 50-65 udp length { 50, 65 } udp length { 35-50 }
checksum <checksum>	UDP checksum	udp checksum 22 udp checksum != 33-45 udp checksum { 33, 55, 67, 88 } udp checksum { 33-55 }

Udplite

udplite match
dport <destination port>	Destination port	udplite dport 22 udplite dport != 33-45 udplite dport { 33-55 } udplite dport { telnet, http, https } udplite dport vmap { 22 : accept, 23 : drop } udplite dport vmap { 25:accept, 28:drop }
sport < source port>	Source port	udplite sport 22 udplite sport != 33-45 udplite sport { 33, 55, 67, 88 } udplite sport { 33-55 } udplite sport vmap { 25:accept, 28:drop } udplite sport 1024 udplite dport 22
checksum <checksum>	Checksum	udplite checksum 22 udplite checksum != 33-45 udplite checksum { 33, 55, 67, 88 } udplite checksum { 33-55 }

Sctp

sctp match
dport <destination port>	Destination port	sctp dport 22 sctp dport != 33-45 sctp dport { 33-55 } sctp dport { telnet, http, https } sctp dport vmap { 22 : accept, 23 : drop } sctp dport vmap { 25:accept, 28:drop }
sport < source port>	Source port	sctp sport 22 sctp sport != 33-45 sctp sport { 33, 55, 67, 88 } sctp sport { 33-55 } sctp sport vmap { 25:accept, 28:drop } sctp sport 1024 sctp dport 22
checksum <checksum>	Checksum	sctp checksum 22 sctp checksum != 33-45 sctp checksum { 33, 55, 67, 88 } sctp checksum { 33-55 }
vtag <tag>	Verification tag	sctp vtag 22 sctp vtag != 33-45 sctp vtag { 33, 55, 67, 88 } sctp vtag { 33-55 }
chunk <type>	Existence of a chunk with given type in packet	sctp chunk init exists sctp chunk error missing
chunk <type> <field>	A chunk's field value (implies chunk existence)	<sourcex lang="bash"> sctp chunk init flags 0x1 sctp chunk data tsn 0x23 </source>

Dccp

dccp match
dport <destination port>	Destination port	dccp dport 22 dccp dport != 33-45 dccp dport { 33-55 } dccp dport { telnet, http, https } dccp dport vmap { 22 : accept, 23 : drop } dccp dport vmap { 25:accept, 28:drop }
sport < source port>	Source port	dccp sport 22 dccp sport != 33-45 dccp sport { 33, 55, 67, 88 } dccp sport { 33-55 } dccp sport vmap { 25:accept, 28:drop } dccp sport 1024 dccp dport 22
type <type>	Type of packet	dccp type { request, response, data, ack, dataack, closereq, close, reset, sync, syncack } dccp type request dccp type != request

Ah

ah match
hdrlength <length>	AH header length	ah hdrlength 11-23 ah hdrlength != 11-23 ah hdrlength { 11, 23, 44 }
reserved <value>		ah reserved 22 ah reserved != 33-45 ah reserved { 23, 100 } ah reserved { 33-55 }
spi <value>		ah spi 111 ah spi != 111-222 ah spi { 111, 122 }
sequence <sequence>	Sequence Number	ah sequence 123 ah sequence { 23, 25, 33 } ah sequence != 23-33

Esp

esp match
spi <value>		esp spi 111 esp spi != 111-222 esp spi { 111, 122 }
sequence <sequence>	Sequence Number	esp sequence 123 esp sequence { 23, 25, 33 } esp sequence != 23-33

Comp

comp match
nexthdr <protocol>	Next header protocol (Upper layer protocol)	comp nexthdr != esp comp nexthdr { esp, ah, comp, udp, udplite, tcp, tcp, dccp, sctp }
flags <flags>	Flags	comp flags 0x0 comp flags != 0x33-0x45 comp flags { 0x33, 0x55, 0x67, 0x88 }
cpi <value>	Compression Parameter Index	comp cpi 22 comp cpi != 33-45 comp cpi { 33, 55, 67, 88 }

Icmp

icmp match
type <type>	ICMP packet type	icmp type { echo-reply, destination-unreachable, source-quench, redirect, echo-request, time-exceeded, parameter-problem, timestamp-request, timestamp-reply, info-request, info-reply, address-mask-request, address-mask-reply, router-advertisement, router-solicitation }
code	ICMP packet code	icmp code 111 icmp code != 33-55 icmp code { 2, 4, 54, 33, 56 }
checksum <value>	ICMP packet checksum	icmp checksum 12343 icmp checksum != 11-343 icmp checksum { 1111, 222, 343 }
id <value>	ICMP packet id	icmp id 12343 icmp id != 11-343 icmp id { 1111, 222, 343 }
sequence <value>	ICMP packet sequence	icmp sequence 12343 icmp sequence != 11-343 icmp sequence { 1111, 222, 343 }
mtu <value>	ICMP packet mtu	icmp mtu 12343 icmp mtu != 11-343 icmp mtu { 1111, 222, 343 }
gateway <value>	ICMP packet gateway	icmp gateway 12343 icmp gateway != 11-343 icmp gateway { 1111, 222, 343 }

Icmpv6

icmpv6 match
type <type>	ICMPv6 packet type	icmpv6 type { destination-unreachable, packet-too-big, time-exceeded, echo-request, echo-reply, mld-listener-query, mld-listener-report, mld-listener-reduction, nd-router-solicit, nd-router-advert, nd-neighbor-solicit, nd-neighbor-advert, parameter-problem, mld2-listener-report }
code	ICMPv6 packet code	icmpv6 code 4 icmpv6 code 3-66 icmpv6 code { 5, 6, 7 }
checksum <value>	ICMPv6 packet checksum	icmpv6 checksum 12343 icmpv6 checksum != 11-343 icmpv6 checksum { 1111, 222, 343 }
id <value>	ICMPv6 packet id	icmpv6 id 12343 icmpv6 id != 11-343 icmpv6 id { 1111, 222, 343 }
sequence <value>	ICMPv6 packet sequence	icmpv6 sequence 12343 icmpv6 sequence != 11-343 icmpv6 sequence { 1111, 222, 343 }
mtu <value>	ICMPv6 packet mtu	icmpv6 mtu 12343 icmpv6 mtu != 11-343 icmpv6 mtu { 1111, 222, 343 }
max-delay <value>	ICMPv6 packet max delay	icmpv6 max-delay 33-45 icmpv6 max-delay != 33-45 icmpv6 max-delay { 33, 55, 67, 88 }

Ether

ether match
saddr <mac address>	Source mac address	ether saddr 00:0f:54:0c:11:04
type <type>		ether type vlan

Dst

dst match
nexthdr <proto>	Next protocol header	dst nexthdr { udplite, ipcomp, udp, ah, sctp, esp, dccp, tcp, ipv6-icmp } dst nexthdr 22 dst nexthdr != 33-45
hdrlength <length>	Header Length	dst hdrlength 22 dst hdrlength != 33-45 dst hdrlength { 33, 55, 67, 88 }

Frag

frag match
nexthdr <proto>	Next protocol header	frag nexthdr { udplite, comp, udp, ah, sctp, esp, dccp, tcp, ipv6-icmp, icmp } frag nexthdr 6 frag nexthdr != 50-51
reserved <value>		frag reserved 22 frag reserved != 33-45 frag reserved { 33, 55, 67, 88 }
frag-off <value>		frag frag-off 22 frag frag-off != 33-45 frag frag-off { 33, 55, 67, 88 }
more-fragments <value>		frag more-fragments 0 frag more-fragments 0
id <value>		frag id 1 frag id 33-45

Hbh

hbh match
nexthdr <proto>	Next protocol header	hbh nexthdr { udplite, comp, udp, ah, sctp, esp, dccp, tcp, icmpv6 } hbh nexthdr 22 hbh nexthdr != 33-45
hdrlength <length>	Header Length	hbh hdrlength 22 hbh hdrlength != 33-45 hbh hdrlength { 33, 55, 67, 88 }

Mh

mh match
nexthdr <proto>	Next protocol header	mh nexthdr { udplite, ipcomp, udp, ah, sctp, esp, dccp, tcp, ipv6-icmp } mh nexthdr 22 mh nexthdr != 33-45
hdrlength <length>	Header Length	mh hdrlength 22 mh hdrlength != 33-45 mh hdrlength { 33, 55, 67, 88 }
type <type>		mh type { binding-refresh-request, home-test-init, careof-test-init, home-test, careof-test, binding-update, binding-acknowledgement, binding-error, fast-binding-update, fast-binding-acknowledgement, fast-binding-advertisement, experimental-mobility-header, home-agent-switch-message } mh type home-agent-switch-message mh type != home-agent-switch-message
reserved <value>		mh reserved 22 mh reserved != 33-45 mh reserved { 33, 55, 67, 88 }
checksum <value>		mh checksum 22 mh checksum != 33-45 mh checksum { 33, 55, 67, 88 }

Rt

rt match
nexthdr <proto>	Next protocol header	rt nexthdr { udplite, ipcomp, udp, ah, sctp, esp, dccp, tcp, ipv6-icmp } rt nexthdr 22 rt nexthdr != 33-45
hdrlength <length>	Header Length	rt hdrlength 22 rt hdrlength != 33-45 rt hdrlength { 33, 55, 67, 88 }
type <type>		rt type 22 rt type != 33-45 rt type { 33, 55, 67, 88 }
seg-left <value>		rt seg-left 22 rt seg-left != 33-45 rt seg-left { 33, 55, 67, 88 }

Vlan

vlan match
id <value>	Vlan tag ID	vlan id 4094 vlan id 0
cfi <value>		vlan cfi 0 vlan cfi 1
pcp <value>		vlan pcp 7 vlan pcp 3

Arp

arp match
ptype <value>	Payload type	arp ptype 0x0800
htype <value>	Header type	arp htype 1 arp htype != 33-45 arp htype { 33, 55, 67, 88 }
hlen <length>	Header Length	arp hlen 1 arp hlen != 33-45 arp hlen { 33, 55, 67, 88 }
plen <length>	Payload length	arp plen 1 arp plen != 33-45 arp plen { 33, 55, 67, 88 }
operation <value>		arp operation { nak, inreply, inrequest, rreply, rrequest, reply, request }

Ct

ct match
state <state>	State of the connection	ct state { new, established, related, untracked } ct state != related ct state established ct state 8
direction <value>	Direction of the packet relative to the connection	ct direction original ct direction != original ct direction { reply, original }
status <status>	Status of the connection	ct status expected (ct status & expected) != expected ct status { expected, seen-reply, assured, confirmed, snat, dnat, dying }
mark [set]	Mark of the connection	ct mark 0 ct mark or 0x23 == 0x11 ct mark or 0x3 != 0x1 ct mark and 0x23 == 0x11 ct mark and 0x3 != 0x1 ct mark xor 0x23 == 0x11 ct mark xor 0x3 != 0x1 ct mark 0x00000032 ct mark != 0x00000032 ct mark 0x00000032-0x00000045 ct mark != 0x00000032-0x00000045 ct mark { 0x32, 0x2222, 0x42de3 } ct mark { 0x32-0x2222, 0x4444-0x42de3 } ct mark set 0x11 xor 0x1331 ct mark set 0x11333 and 0x11 ct mark set 0x12 or 0x11 ct mark set 0x11 ct mark set mark ct mark set mark map { 1 : 10, 2 : 20, 3 : 30 }
expiration	Connection expiration time	ct expiration 30 ct expiration 30s ct expiration != 233 ct expiration != 3m53s ct expiration 33-45 ct expiration 33s-45s ct expiration != 33-45 ct expiration != 33s-45s ct expiration { 33, 55, 67, 88 } ct expiration { 1m7s, 33s, 55s, 1m28s }
helper "<helper>"	Helper associated with the connection	ct helper "ftp"
[original | reply] bytes <value>		ct original bytes > 100000 ct bytes > 100000
[original | reply] packets <value>		ct reply packets < 100
[original | reply] ip saddr <ip source address>		ct original ip saddr 192.168.0.1 ct reply ip saddr 192.168.0.1 ct original ip saddr 192.168.1.0/24 ct reply ip saddr 192.168.1.0/24
[original | reply] ip daddr <ip destination address>		ct original ip daddr 192.168.0.1 ct reply ip daddr 192.168.0.1 ct original ip daddr 192.168.1.0/24 ct reply ip daddr 192.168.1.0/24
[original | reply] l3proto <protocol>		ct original l3proto ipv4
[original | reply] protocol <protocol>		ct original protocol 6
[original | reply] proto-dst <port>		ct original proto-dst 22
[original | reply] proto-src <port>		ct reply proto-src 53
count [over] <number of connections>		ct count over 2 tcp dport 22 add @ssh_flood { ip saddr ct count over 2 } reject [ which requires an existing ssh_flood set, ie. add set filter ssh_flood { type ipv4_addr; flags dynamic; } ]

Meta

meta matches packet by metainformation.

meta match
iifname <input interface name>	Input interface name	meta iifname "eth0" meta iifname != "eth0" meta iifname { "eth0", "lo" } meta iifname "eth*"
oifname <output interface name>	Output interface name	meta oifname "eth0" meta oifname != "eth0" meta oifname { "eth0", "lo" } meta oifname "eth*"
iif <input interface index>	Input interface index	meta iif eth0 meta iif != eth0
oif <output interface index>	Output interface index	meta oif lo meta oif != lo meta oif { eth0, lo }
iiftype <input interface type>	Input interface type	meta iiftype { ether, ppp, ipip, ipip6, loopback, sit, ipgre } meta iiftype != ether meta iiftype ether
oiftype <output interface type>	Output interface hardware type	meta oiftype { ether, ppp, ipip, ipip6, loopback, sit, ipgre } meta oiftype != ether meta oiftype ether
length <length>	Length of the packet in bytes	meta length 1000 meta length != 1000 meta length > 1000 meta length 33-45 meta length != 33-45 meta length { 33, 55, 67, 88 } meta length { 33-55, 67-88 }
protocol <protocol>	ethertype protocol	meta protocol ip meta protocol != ip meta protocol { ip, arp, ip6, vlan }
nfproto <protocol>		meta nfproto ipv4 meta nfproto != ipv6 meta nfproto { ipv4, ipv6 }
l4proto <protocol>		meta l4proto 22 meta l4proto != 233 meta l4proto 33-45 meta l4proto { 33, 55, 67, 88 } meta l4proto { 33-55 }
mark [set]	Packet mark	meta mark 0x4 meta mark 0x00000032 meta mark and 0x03 == 0x01 meta mark and 0x03 != 0x01 meta mark != 0x10 meta mark or 0x03 == 0x01 meta mark or 0x03 != 0x01 meta mark xor 0x03 == 0x01 meta mark xor 0x03 != 0x01 meta mark set 0xffffffc8 xor 0x16 meta mark set 0x16 and 0x16 meta mark set 0xffffffe9 or 0x16 meta mark set 0xffffffde and 0x16 meta mark set 0x32 or 0xfffff meta mark set 0xfffe xor 0x16
priority [set] <priority>	tc class id	meta priority none meta priority 0x1:0x1 meta priority 0x1:0xffff meta priority 0xffff:0xffff meta priority set 0x1:0x1 meta priority set 0x1:0xffff meta priority set 0xffff:0xffff
skuid <user id>	UID associated with originating socket	meta skuid { bin, root, daemon } meta skuid root meta skuid != root meta skuid lt 3000 meta skuid gt 3000 meta skuid eq 3000 meta skuid 3001-3005 meta skuid != 2001-2005 meta skuid { 2001-2005 }
skgid <group id>	GID associated with originating socket	meta skgid { bin, root, daemon } meta skgid root meta skgid != root meta skgid lt 3000 meta skgid gt 3000 meta skgid eq 3000 meta skgid 3001-3005 meta skgid != 2001-2005 meta skgid { 2001-2005 }
rtclassid <class>	Routing realm	meta rtclassid cosmos
pkttype <type>	Packet type	meta pkttype broadcast meta pkttype != broadcast meta pkttype { broadcast, unicast, multicast }
cpu <cpu index>	CPU ID	meta cpu 1 meta cpu != 1 meta cpu 1-3 meta cpu != 1-2 meta cpu { 2,3 } meta cpu { 2-3, 5-7 }
iifgroup <input group>	Input interface group	meta iifgroup 0 meta iifgroup != 0 meta iifgroup default meta iifgroup != default meta iifgroup { default } meta iifgroup { 11,33 } meta iifgroup { 11-33 }
oifgroup <group>	Output interface group	meta oifgroup 0 meta oifgroup != 0 meta oifgroup default meta oifgroup != default meta oifgroup { default } meta oifgroup { 11,33 } meta oifgroup { 11-33 }
cgroup <group>		meta cgroup 1048577 meta cgroup != 1048577 meta cgroup { 1048577, 1048578 } meta cgroup 1048577-1048578 meta cgroup != 1048577-1048578 meta cgroup { 1048577-1048578 }

Statements

statement is the action performed when the packet match the rule. It could be terminal and non-terminal. In a certain rule we can consider several non-terminal statements but only a single terminal statement.

Verdict statements

The verdict statement alters control flow in the ruleset and issues policy decisions for packets. The valid verdict statements are:

• accept: Accept the packet and stop the remain rules evaluation.
• drop: Drop the packet and stop the remain rules evaluation.
• queue: Queue the packet to userspace and stop the remain rules evaluation.
• continue: Continue the ruleset evaluation with the next rule.
• return: Return from the current chain and continue at the next rule of the last chain. In a base chain it is equivalent to accept
• jump <chain>: Continue at the first rule of <chain>. It will continue at the next rule after a return statement is issued
• goto <chain>: Similar to jump, but after the new chain the evaluation will continue at the last chain instead of the one containing the goto statement

Log

log statement
level [over] <value> <unit> [burst <value> <unit>]	Log level	log log level emerg log level alert log level crit log level err log level warn log level notice log level info log level debug
group <value> [queue-threshold <value>] [snaplen <value>] [prefix "<prefix>"]		log prefix aaaaa-aaaaaa group 2 snaplen 33 log group 2 queue-threshold 2 log group 2 snaplen 33

Reject

The default reject will be the ICMP type port-unreachable. The icmpx is only used for inet family support.

More information on the Rejecting_traffic page.

reject statement
with <protocol> type <type>		reject reject with icmp type host-unreachable reject with icmp type net-unreachable reject with icmp type prot-unreachable reject with icmp type port-unreachable reject with icmp type net-prohibited reject with icmp type host-prohibited reject with icmp type admin-prohibited reject with icmpv6 type no-route reject with icmpv6 type admin-prohibited reject with icmpv6 type addr-unreachable reject with icmpv6 type port-unreachable reject with icmpx type host-unreachable reject with icmpx type no-route reject with icmpx type admin-prohibited reject with icmpx type port-unreachable ip protocol tcp reject with tcp reset

Counter

counter statement
packets <packets> bytes <bytes>		counter counter packets 0 bytes 0

Limit

limit statement
rate [over] <value> <unit> [burst <value> <unit>]	Rate limit	limit rate 400/minute limit rate 400/hour limit rate over 40/day limit rate over 400/week limit rate over 1023/second burst 10 packets limit rate 1025 kbytes/second limit rate 1023000 mbytes/second limit rate 1025 bytes/second burst 512 bytes limit rate 1025 kbytes/second burst 1023 kbytes limit rate 1025 mbytes/second burst 1025 kbytes limit rate 1025000 mbytes/second burst 1023 mbytes

Nat

nat statement
dnat to <destination address>	Destination address translation	dnat to 192.168.3.2 dnat to ct mark map { 0x00000014 : 1.2.3.4 }
snat to <ip source address>	Source address translation	snat to 192.168.3.2 snat to 2001:838:35f:1::-2001:838:35f:2:::100
masquerade [<type>] [to :<port>]	Masquerade	masquerade masquerade persistent,fully-random,random masquerade to :1024 masquerade to :1024-2048

Queue

queue statement
num <value> <scheduler>		queue queue num 2 queue num 2-3 queue num 4-5 fanout bypass queue num 4-5 fanout queue num 4-5 bypass

Extras

Export Configuration

% nft export (xml | json)

Monitor Events

Monitor events from Netlink creating filters.

% nft monitor [new | destroy] [tables | chains | sets | rules | elements] [xml | json]

Nft scripting

List ruleset

% nft list ruleset

Flush ruleset

% nft flush ruleset

Load ruleset

Create a command batch file and load it with the nft interpreter,

% echo "flush ruleset" > /etc/nftables.rules
% echo "add table filter" >> /etc/nftables.rules
% echo "add chain filter input" >> /etc/nftables.rules
% echo "add rule filter input meta iifname lo accept" >> /etc/nftables.rules
% nft -f /etc/nftables.rules

or create an executable nft script file,

% cat << EOF > /etc/nftables.rules
> #!/usr/local/sbin/nft -f
> flush ruleset
> add table filter
> add chain filter input
> add rule filter input meta iifname lo accept
> EOF
% chmod u+x /etc/nftables.rules
% /etc/nftables.rules

or create an executable nft script file from an already created ruleset,

% nft list ruleset > /etc/nftables.rules
% nft flush ruleset
% nft -f /etc/nftables.rules

Examples

Simple IP/IPv6 Firewall

flush ruleset

table firewall {
  chain incoming {
    type filter hook input priority 0; policy drop;

    # established/related connections
    ct state established,related accept

    # loopback interface
    iifname lo accept

    # icmp
    icmp type echo-request accept

    # open tcp ports: sshd (22), httpd (80)
    tcp dport { ssh, http } accept
  }
}

table ip6 firewall {
  chain incoming {
    type filter hook input priority 0; policy drop;

    # established/related connections
    ct state established,related accept

    # invalid connections
    ct state invalid drop

    # loopback interface
    iifname lo accept

    # icmp
    # routers may also want: mld-listener-query, nd-router-solicit
    icmpv6 type { echo-request, nd-neighbor-solicit } accept

    # open tcp ports: sshd (22), httpd (80)
    tcp dport { ssh, http } accept
  }
}