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nft(8) - phpMan
nft(8) nft(8)
NAME
nft - Administration tool for packet filtering and classification
SYNOPSIS
nft [ -n | --numeric ] [ [-I | --includepath] directory ] [ [-f | --file] filename | [-i |
--interactive] | cmd ...]
nft [ -h | --help ] [ -v | --version ]
DESCRIPTION
nft is used to set up, maintain and inspect packet filtering and classification rules in
the Linux kernel.
OPTIONS
For a full summary of options, run nft --help.
-h, --help
Show help message and all options.
-v, --version
Show version.
-n, --numeric
Numeric output: Addresses and other information that might need network traffic to
resolve to symbolic names are shown numerically (default behaviour). When used
twice, internet services are translated. When used twice, internet services and
UIDs/GIDs are also shown numerically. When used three times, protocol numbers are
also shown numerically.
-N Translate IP addresses to DNS names.
-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 FILE FORMAT
LEXICAL CONVENTIONS
Input is parsed line-wise. When the last character of a line, just before the newline
character, is a non-quoted backslash (\), the next line is treated as a continuation. Mul‐
tiple 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 alphanu‐
meric characters (a-z,A-Z,0-9) and the characters slash (/), backslash (\), underscore (_)
and dot (.). Identifiers using different characters or clashing with a keyword need to be
enclosed in double quotes (").
INCLUDE FILES
include filename
Other files can be included by using the include statement. The directories to be
searched for include files can be specified using the -I/--includepath option.
SYMBOLIC VARIABLES
define variable expr
$variable
Symbolic variables can be defined using the define statement. Variable references are ex‐
pressions and can be used initialize other variables. The scope of a definition is the
current block and all blocks contained within.
Using symbolic variables
define int_if1 = eth0
define int_if2 = eth1
define int_ifs = { $int_if1, $int_if2 }
filter input iif $int_ifs accept
ADDRESS FAMILIES
Address families determine the type of packets which are processed. For each address fami‐
ly 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 identi‐
fiers include an address family. If an identifier is specified without an address family,
the ip family is used by default.
IPV4/IPV6/INET ADDRESS FAMILIES
The IPv4/IPv6/Inet address families handle IPv4, IPv6 or both types of packets. They con‐
tain five hooks at different packet processing stages in the network stack.
IPv4/IPv6/Inet address family hooks
┌────────────┬──────────────────────────────────┐
│Hook │ Description │
├────────────┼──────────────────────────────────┤
│prerouting │ All packets entering the system │
│ │ are processed by the prerouting │
│ │ hook. It is invoked before the │
│ │ routing process and is used for │
│ │ early filtering or changing │
│ │ packet attributes that affect │
│ │ routing. │
├────────────┼──────────────────────────────────┤
│input │ Packets delivered to the local │
│ │ system are processed by the in‐ │
│ │ put hook. │
├────────────┼──────────────────────────────────┤
│forward │ Packets forwarded to a different │
│ │ host are processed by the for‐ │
│ │ ward 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. │
└────────────┴──────────────────────────────────┘
ARP ADDRESS FAMILY
The ARP address family handles ARP packets received and sent by the system. It is commonly
used to mangle ARP packets for clustering.
ARP address family hooks
┌───────┬──────────────────────────────────┐
│Hook │ Description │
├───────┼──────────────────────────────────┤
│input │ Packets delivered to the local │
│ │ system are processed by the in‐ │
│ │ put hook. │
├───────┼──────────────────────────────────┤
│output │ Packets send by the local system │
│ │ are processed by the output │
│ │ hook. │
└───────┴──────────────────────────────────┘
BRIDGE ADDRESS FAMILY
The bridge address family handles ethernet packets traversing bridge devices.
NETDEV ADDRESS FAMILY
The Netdev address family handles packets from ingress.
Netdev address family hooks
┌────────┬──────────────────────────────────┐
│Hook │ Description │
├────────┼──────────────────────────────────┤
│ingress │ All packets entering the system │
│ │ are processed by this hook. It │
│ │ is invoked before layer 3 proto‐ │
│ │ col handlers and it can be used │
│ │ for early filtering and polic‐ │
│ │ ing. │
└────────┴──────────────────────────────────┘
TABLES
{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 in‐
et 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.
CHAINS
{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 speci‐
fied, 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.
RULES
[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
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 rela‐
tional (match) expressions. They are also used as arguments to certain types of opera‐
tions, like NAT, packet marking etc.
Each expression has a data type, which determines the size, parsing and representation of
symbolic values and type compatibility with other expressions.
DESCRIBE COMMAND
describe {expression}
The describe command shows information about the type of an expression and its data type.
The describe command
$ 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
Data types determine the size, parsing and representation of symbolic values and type com‐
patibility of expressions. A number of global data types exist, in addition some expres‐
sion 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.
INTEGER TYPE
┌────────┬─────────┬──────────┬───────────┐
│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.
BITMASK TYPE
┌────────┬─────────┬──────────┬───────────┐
│Name │ Keyword │ Size │ Base type │
├────────┼─────────┼──────────┼───────────┤
│Bitmask │ bitmask │ variable │ integer │
└────────┴─────────┴──────────┴───────────┘
The bitmask type (bitmask) is used for bitmasks.
STRING TYPE
┌───────┬─────────┬──────────┬───────────┐
│Name │ Keyword │ Size │ Base type │
├───────┼─────────┼──────────┼───────────┤
│String │ string │ variable │ - │
└───────┴─────────┴──────────┴───────────┘
The string type is used to for character strings. A string begins with an alphabetic char‐
acter (a-zA-Z) followed by zero or more alphanumeric characters or the characters /, -, _
and .. In addition anything enclosed in double quotes (") is recognized as a string.
String specification
# Interface name
filter input iifname eth0
# Weird interface name
filter input iifname "(eth0)"
LINK LAYER ADDRESS TYPE
┌───────────────────┬─────────┬──────────┬───────────┐
│Name │ Keyword │ Size │ Base type │
├───────────────────┼─────────┼──────────┼───────────┤
│Link layer address │ lladdr │ variable │ integer │
└───────────────────┴─────────┴──────────┴───────────┘
The link layer address type is used for link layer addresses. Link layer addresses are
specified as a variable amount of groups of two hexadecimal digits separated using colons
(:).
Link layer address specification
# Ethernet destination MAC address
filter input ether daddr 20:c9:d0:43:12:d9
IPV4 ADDRESS TYPE
┌─────────────┬───────────┬────────┬───────────┐
│Name │ Keyword │ Size │ Base type │
├─────────────┼───────────┼────────┼───────────┤
│IPv4 address │ ipv4_addr │ 32 bit │ integer │
└─────────────┴───────────┴────────┴───────────┘
The IPv4 address type is used for IPv4 addresses. Addresses are specified in either dotted
decimal, dotted hexadecimal, dotted octal, decimal, hexadecimal, octal notation or as a
host name. A host name will be resolved using the standard system resolver.
IPv4 address specification
# dotted decimal notation
filter output ip daddr 127.0.0.1
# host name
filter output ip daddr localhost
IPV6 ADDRESS TYPE
┌─────────────┬───────────┬─────────┬───────────┐
│Name │ Keyword │ Size │ Base type │
├─────────────┼───────────┼─────────┼───────────┤
│IPv6 address │ ipv6_addr │ 128 bit │ integer │
└─────────────┴───────────┴─────────┴───────────┘
The IPv6 address type is used for IPv6 addresses. FIXME
IPv6 address specification
# abbreviated loopback address
filter output ip6 daddr ::1
PRIMARY EXPRESSIONS
The lowest order expression is a primary expression, representing either a constant or a
single datum from a packet's payload, meta data or a stateful module.
META EXPRESSIONS
meta {length | nfproto | l4proto | protocol | priority}
[meta] {mark | iif | iifname | iiftype | oif | oifname | oiftype | skuid | skgid | nftrace
| rtclassid | ibriport | obriport | pkttype | cpu | iifgroup | oifgroup | cgroup}
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 expres‐
sions.
Meta expression types
┌──────────┬──────────────────────────┬───────────────────┐
│Keyword │ Description │ Type │
├──────────┼──────────────────────────┼───────────────────┤
│length │ Length of the packet in │ integer (32 bit) │
│ │ bytes │ │
├──────────┼──────────────────────────┼───────────────────┤
│protocol │ Ethertype protocol value │ ether_type │
├──────────┼──────────────────────────┼───────────────────┤
│priority │ TC packet priority │ integer (32 bit) │
├──────────┼──────────────────────────┼───────────────────┤
│mark │ Packet mark │ packetmark │
├──────────┼──────────────────────────┼───────────────────┤
│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 hard‐ │ iface_type │
│ │ ware type │ │
├──────────┼──────────────────────────┼───────────────────┤
│skuid │ UID associated with │ uid │
│ │ originating socket │ │
├──────────┼──────────────────────────┼───────────────────┤
│skgid │ GID associated with │ gid │
│ │ originating socket │ │
├──────────┼──────────────────────────┼───────────────────┤
│rtclassid │ Routing realm │ realm │
├──────────┼──────────────────────────┼───────────────────┤
│ibriport │ Input bridge interface │ string │
│ │ name │ │
├──────────┼──────────────────────────┼───────────────────┤
│obriport │ Output bridge interface │ string │
│ │ name │ │
├──────────┼──────────────────────────┼───────────────────┤
│pkttype │ packet type │ pkt_type │
├──────────┼──────────────────────────┼───────────────────┤
│cpu │ cpu number processing │ integer (32 bits) │
│ │ the packet │ │
├──────────┼──────────────────────────┼───────────────────┤
│iifgroup │ incoming device group │ devgroup_type │
├──────────┼──────────────────────────┼───────────────────┤
│oifgroup │ outgoing device group │ devgroup_type │
├──────────┼──────────────────────────┼───────────────────┤
│cgroup │ control group id │ integer (32 bits) │
└──────────┴──────────────────────────┴───────────────────┘
Meta expression specific types
┌──────────────┬──────────────────────────────────┐
│Type │ Description │
├──────────────┼──────────────────────────────────┤
│iface_index │ Interface index (32 bit number). │
│ │ Can be specified numerically or │
│ │ as name of an existing inter‐ │
│ │ face. │
├──────────────┼──────────────────────────────────┤
│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). │
└──────────────┴──────────────────────────────────┘
Using meta expressions
# qualified meta expression
filter output meta oif eth0
# unqualified meta expression
filter output oif eth0
PAYLOAD EXPRESSIONS
Payload expressions refer to data from the packet's payload.
ETHERNET HEADER EXPRESSION
ether [ethernet header field]
Ethernet header expression types
┌────────┬─────────────────────────┬────────────┐
│Keyword │ Description │ Type │
├────────┼─────────────────────────┼────────────┤
│daddr │ Destination MAC address │ ether_addr │
├────────┼─────────────────────────┼────────────┤
│saddr │ Source MAC address │ ether_addr │
├────────┼─────────────────────────┼────────────┤
│type │ EtherType │ ether_type │
└────────┴─────────────────────────┴────────────┘
VLAN HEADER EXPRESSION
vlan [VLAN header field]
VLAN header expression
┌────────┬──────────────────────────┬──────────────────┐
│Keyword │ Description │ Type │
├────────┼──────────────────────────┼──────────────────┤
│id │ VLAN ID (VID) │ integer (12 bit) │
├────────┼──────────────────────────┼──────────────────┤
│cfi │ Canonical Format Indica‐ │ flag │
│ │ tor │ │
├────────┼──────────────────────────┼──────────────────┤
│pcp │ Priority code point │ integer (3 bit) │
├────────┼──────────────────────────┼──────────────────┤
│type │ EtherType │ ethertype │
└────────┴──────────────────────────┴──────────────────┘
ARP HEADER EXPRESSION
arp [ARP header field]
ARP header expression
┌──────────┬──────────────────────┬──────────────────┐
│Keyword │ Description │ Type │
├──────────┼──────────────────────┼──────────────────┤
│htype │ ARP hardware type │ integer (16 bit) │
├──────────┼──────────────────────┼──────────────────┤
│ptype │ EtherType │ ethertype │
├──────────┼──────────────────────┼──────────────────┤
│hlen │ Hardware address len │ integer (8 bit) │
├──────────┼──────────────────────┼──────────────────┤
│plen │ Protocol address len │ integer (8 bit) │
├──────────┼──────────────────────┼──────────────────┤
│operation │ Operation │ arp_op │
└──────────┴──────────────────────┴──────────────────┘
IPV4 HEADER EXPRESSION
ip [IPv4 header field]
IPv4 header expression
┌──────────┬──────────────────────────┬──────────────────────────┐
│Keyword │ Description │ Type │
├──────────┼──────────────────────────┼──────────────────────────┤
│version │ IP header version (4) │ integer (4 bit) │
├──────────┼──────────────────────────┼──────────────────────────┤
│hdrlength │ IP header length includ‐ │ integer (4 bit) FIXME │
│ │ ing options │ scaling │
├──────────┼──────────────────────────┼──────────────────────────┤
│dscp │ Differentiated Services │ integer (6 bit) │
│ │ Code Point │ │
├──────────┼──────────────────────────┼──────────────────────────┤
│ecn │ Explicit Congestion No‐ │ integer (2 bit) │
│ │ tification │ │
├──────────┼──────────────────────────┼──────────────────────────┤
│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 │
└──────────┴──────────────────────────┴──────────────────────────┘
IPV6 HEADER EXPRESSION
ip6 [IPv6 header field]
IPv6 header expression
┌──────────┬──────────────────────────┬──────────────────┐
│Keyword │ Description │ Type │
├──────────┼──────────────────────────┼──────────────────┤
│version │ IP header version (6) │ integer (4 bit) │
├──────────┼──────────────────────────┼──────────────────┤
│priority │ │ │
├──────────┼──────────────────────────┼──────────────────┤
│dscp │ Differentiated Services │ integer (6 bit) │
│ │ Code Point │ │
├──────────┼──────────────────────────┼──────────────────┤
│ecn │ Explicit Congestion No‐ │ integer (2 bit) │
│ │ tification │ │
├──────────┼──────────────────────────┼──────────────────┤
│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 HEADER EXPRESSION
tcp [TCP header field]
TCP header expression
┌─────────┬────────────────────────┬──────────────────────────┐
│Keyword │ Description │ Type │
├─────────┼────────────────────────┼──────────────────────────┤
│sport │ Source port │ inet_service │
├─────────┼────────────────────────┼──────────────────────────┤
│dport │ Destination port │ inet_service │
├─────────┼────────────────────────┼──────────────────────────┤
│sequence │ Sequence number │ integer (32 bit) │
├─────────┼────────────────────────┼──────────────────────────┤
│ackseq │ Acknowledgement number │ integer (32 bit) │
├─────────┼────────────────────────┼──────────────────────────┤
│doff │ Data offset │ integer (4 bit) FIXME │
│ │ │ scaling │
├─────────┼────────────────────────┼──────────────────────────┤
│reserved │ Reserved area │ integer (4 bit) │
├─────────┼────────────────────────┼──────────────────────────┤
│flags │ TCP flags │ tcp_flags │
├─────────┼────────────────────────┼──────────────────────────┤
│window │ Window │ integer (16 bit) │
├─────────┼────────────────────────┼──────────────────────────┤
│checksum │ Checksum │ integer (16 bit) │
├─────────┼────────────────────────┼──────────────────────────┤
│urgptr │ Urgent pointer │ integer (16 bit) │
└─────────┴────────────────────────┴──────────────────────────┘
UDP HEADER EXPRESSION
udp [UDP header field]
UDP header expression
┌─────────┬─────────────────────┬──────────────────┐
│Keyword │ Description │ Type │
├─────────┼─────────────────────┼──────────────────┤
│sport │ Source port │ inet_service │
├─────────┼─────────────────────┼──────────────────┤
│dport │ Destination port │ inet_service │
├─────────┼─────────────────────┼──────────────────┤
│length │ Total packet length │ integer (16 bit) │
├─────────┼─────────────────────┼──────────────────┤
│checksum │ Checksum │ integer (16 bit) │
└─────────┴─────────────────────┴──────────────────┘
UDP-LITE HEADER EXPRESSION
udplite [UDP-Lite header field]
UDP-Lite header expression
┌─────────┬───────────────────┬──────────────────┐
│Keyword │ Description │ Type │
├─────────┼───────────────────┼──────────────────┤
│sport │ Source port │ inet_service │
├─────────┼───────────────────┼──────────────────┤
│dport │ Destination port │ inet_service │
├─────────┼───────────────────┼──────────────────┤
│cscov │ Checksum coverage │ integer (16 bit) │
├─────────┼───────────────────┼──────────────────┤
│checksum │ Checksum │ integer (16 bit) │
└─────────┴───────────────────┴──────────────────┘
SCTP HEADER EXPRESSION
sctp [SCTP header field]
SCTP header expression
┌─────────┬──────────────────┬──────────────────┐
│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 HEADER EXPRESSION
dccp [DCCP header field]
DCCP header expression
┌────────┬──────────────────┬──────────────┐
│Keyword │ Description │ Type │
├────────┼──────────────────┼──────────────┤
│sport │ Source port │ inet_service │
├────────┼──────────────────┼──────────────┤
│dport │ Destination port │ inet_service │
└────────┴──────────────────┴──────────────┘
AUTHENTICATION HEADER EXPRESSION
ah [AH header field]
AH header expression
┌──────────┬──────────────────────────┬──────────────────┐
│Keyword │ Description │ Type │
├──────────┼──────────────────────────┼──────────────────┤
│nexthdr │ Next header protocol │ inet_service │
├──────────┼──────────────────────────┼──────────────────┤
│hdrlength │ AH Header length │ integer (8 bit) │
├──────────┼──────────────────────────┼──────────────────┤
│reserved │ Reserved area │ integer (4 bit) │
├──────────┼──────────────────────────┼──────────────────┤
│spi │ Security Parameter Index │ integer (32 bit) │
├──────────┼──────────────────────────┼──────────────────┤
│sequence │ Sequence number │ integer (32 bit) │
└──────────┴──────────────────────────┴──────────────────┘
ENCRYPTED SECURITY PAYLOAD HEADER EXPRESSION
esp [ESP header field]
ESP header expression
┌─────────┬──────────────────────────┬──────────────────┐
│Keyword │ Description │ Type │
├─────────┼──────────────────────────┼──────────────────┤
│spi │ Security Parameter Index │ integer (32 bit) │
├─────────┼──────────────────────────┼──────────────────┤
│sequence │ Sequence number │ integer (32 bit) │
└─────────┴──────────────────────────┴──────────────────┘
IPCOMP HEADER EXPRESSION
comp [IPComp header field]
IPComp header expression
┌────────┬──────────────────────────┬──────────────────┐
│Keyword │ Description │ Type │
├────────┼──────────────────────────┼──────────────────┤
│nexthdr │ Next header protocol │ inet_service │
├────────┼──────────────────────────┼──────────────────┤
│flags │ Flags │ bitmask │
├────────┼──────────────────────────┼──────────────────┤
│cpi │ Compression Parameter │ integer (16 bit) │
│ │ Index │ │
└────────┴──────────────────────────┴──────────────────┘
BLA
IPV6 EXTENSION HEADER EXPRESSIONS
IPv6 extension header expressions refer to data from an IPv6 packet's extension headers.
CONNTRACK EXPRESSIONS
Conntrack expressions refer to meta data of the connection tracking entry associated with
a packet.
There are three types of conntrack expressions. Some conntrack expressions require the
flow direction before the conntrack key, others must be used directly because they are di‐
rection agnostic. The packets and bytes 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 | bytes | packets}
{original | reply | {l3proto | protocol | saddr | daddr | proto-src | proto-dst | bytes
| packets}}
Conntrack expressions
┌───────────┬──────────────────────────┬─────────────────────┐
│Keyword │ Description │ Type │
├───────────┼──────────────────────────┼─────────────────────┤
│state │ State of the connection │ ct_state │
├───────────┼──────────────────────────┼─────────────────────┤
│direction │ Direction of the packet │ ct_dir │
│ │ relative to the connec‐ │ │
│ │ tion │ │
├───────────┼──────────────────────────┼─────────────────────┤
│status │ Status of the connection │ ct_status │
├───────────┼──────────────────────────┼─────────────────────┤
│mark │ Connection mark │ packetmark │
├───────────┼──────────────────────────┼─────────────────────┤
│expiration │ Connection expiration │ time │
│ │ time │ │
├───────────┼──────────────────────────┼─────────────────────┤
│helper │ Helper associated with │ string │
│ │ the connection │ │
├───────────┼──────────────────────────┼─────────────────────┤
│label │ Connection tracking la‐ │ ct_label │
│ │ bel │ │
├───────────┼──────────────────────────┼─────────────────────┤
│l3proto │ Layer 3 protocol of the │ nf_proto │
│ │ connection │ │
├───────────┼──────────────────────────┼─────────────────────┤
│saddr │ Source address of the │ ipv4_addr/ipv6_addr │
│ │ connection for the given │ │
│ │ direction │ │
├───────────┼──────────────────────────┼─────────────────────┤
│daddr │ Destination address of │ ipv4_addr/ipv6_addr │
│ │ the connection for the │ │
│ │ given direction │ │
├───────────┼──────────────────────────┼─────────────────────┤
│protocol │ Layer 4 protocol of the │ inet_proto │
│ │ connection for the given │ │
│ │ direction │ │
├───────────┼──────────────────────────┼─────────────────────┤
│proto-src │ Layer 4 protocol source │ integer (16 bit) │
│ │ for the given direction │ │
├───────────┼──────────────────────────┼─────────────────────┤
│proto-dst │ Layer 4 protocol desti‐ │ integer (16 bit) │
│ │ nation for the given di‐ │ │
│ │ rection │ │
├───────────┼──────────────────────────┼─────────────────────┤
│packets │ packet count seen in the │ integer (64 bit) │
│ │ given direction or sum │ │
│ │ of original and reply │ │
├───────────┼──────────────────────────┼─────────────────────┤
│bytes │ bytecount seen, see de‐ │ integer (64 bit) │
│ │ scription for packets │ │
│ │ keyword │ │
└───────────┴──────────────────────────┴─────────────────────┘
STATEMENTS
Statements represent actions to be performed. They can alter control flow (return, jump to
a different chain, accept or drop the packet) or can perform actions, such as logging, re‐
jecting 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 evalua‐
tion perspective. There can be an arbitrary amount of non-terminal statements in a rule,
but only a single terminal statement as the final statement.
VERDICT STATEMENT
The verdict statement alters control flow in the ruleset and issues policy decisions for
packets.
{accept | drop | queue | continue | return}
{jump | goto} {chain}
accept 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 rule‐
set 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.
Verdict statements
# process packets from eth0 and the internal network in from_lan
# chain, drop all packets from eth0 with different source addresses.
filter input iif eth0 ip saddr 192.168.0.0/24 jump from_lan
filter input iif eth0 drop
LOG STATEMENT
REJECT STATEMENT
COUNTER STATEMENT
META STATEMENT
LIMIT STATEMENT
NAT STATEMENT
QUEUE STATEMENT
ADDITIONAL COMMANDS
These are some additional commands included in nft.
EXPORT
Export your current ruleset in XML or JSON format to stdout.
Examples:
% nft export xml
[...]
% nft export json
[...]
MONITOR
The monitor command allows you to listen to Netlink events produced by the nf_tables sub‐
system, 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.
Listen to all events, report in native nft format
% nft monitor
Listen to added tables, report in XML format
% nft monitor new tables xml
Listen to deleted rules, report in JSON format
% nft monitor destroy rules json
Listen to both new and destroyed chains, in native nft format
% nft monitor chains
ERROR REPORTING
When an error is detected, nft shows the line(s) containing the error, the position of the
erroneous parts in the input stream and marks up the erroneous parts using 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.
Error caused by single incorrect expression
<cmdline>:1:19-22: Error: Interface does not exist
filter output oif eth0
^^^^
Error caused by invalid combination of two expressions
<cmdline>:1:28-36: Error: Right hand side of relational expression (==) must be constant
filter output tcp dport == tcp dport
~~ ^^^^^^^^^
Error returned by the kernel
<cmdline>:0:0-23: Error: Could not process rule: Operation not permitted
filter output oif wlan0
^^^^^^^^^^^^^^^^^^^^^^^
EXIT STATUS
On success, nft exits with a status of 0. Unspecified errors cause it to exit with a sta‐
tus of 1, memory allocation errors with a status of 2, unable to open Netlink socket with
3.
SEE ALSO
iptables(8), ip6tables(8), arptables(8), ebtables(8), ip(8), tc(8)
There is an official wiki at: http://wiki.nftables.org
AUTHORS
nftables was written by Patrick McHardy.
COPYRIGHT
Copyright 2008-2014 Patrick McHardy <kaber AT trash.net>
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-Share‐
Alike 4.0 license, CC BY-SA 4.0 ⟨http://creativecommons.org/licenses/by-sa/4.0/⟩ .
18 June 2016 nft(8)
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