Provided by: nftables_0.5+snapshot20151106-1_amd64 
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 ker‐
nel.
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 sym‐
bolic 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 by 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. 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 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 expressions 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 family the kernel
contains so called hooks at specific stages of the packet processing paths, which invoke nftables if
rules for these hooks exist.
ip IPv4 address family.
ip6 IPv6 address family.
inet Internet (IPv4/IPv6) address family.
arp ARP address family, handling packets vi
bridge Bridge address family, handling packets which traverse a bridge device.
netdev Netdev address family, handling packets from ingress.
All nftables objects exist in address family specific namespaces, therefore all identifiers include an
address family. If an identifier is specified without an address family, the ip family is used by de‐
fault.
IPV4/IPV6/INET ADDRESS FAMILIES
The IPv4/IPv6/Inet address families handle IPv4, IPv6 or both types of packets. They contain five hooks
at different packet processing stages in the network stack.
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 af‐ │
│ │ fect 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. │
└─────────────┴───────────────────────────────────────┘
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 input hook. │
├────────┼───────────────────────────────────────┤
│ output │ Packets send by the local system are │
│ │ processed by the output hook. │
└────────┴───────────────────────────────────────┘
BRIDGE ADDRESS FAMILY
The bridge address family handles ethernet packets traversing bridge devices.
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 protocol handlers and │
│ │ it can be used for early filtering │
│ │ and policing. │
└─────────┴───────────────────────────────────────┘
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 inet address family is a dummy
family which is used to create hybrid IPv4/IPv6 tables. When no address family is specified, ip is used
by default.
add Add a new table for the given family with the given name.
delete Delete the specified table.
list List all chains and rules of the specified table.
flush Flush all chains and rules of the specified table.
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 specified, the chain is
created as a base chain and hooked up to the networking stack.
create Simlar to the add command, but returns an error if the chain already exists.
delete Delete the specified chain. The chain must not contain any rules or be used as jump target.
rename Rename the specified chain.
list List all rules of the specified chain.
flush Flush all rules of the specified chain.
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 relational (match) expressions. They are also used as
arguments to certain types of operations, like NAT, packet marking etc.
Each expression has a data type, which determines the size, parsing and representation of symbolic values
and type compatibility with other expressions.
DESCRIBE COMMAND
describe {expression}
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 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.
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 character (a-zA-Z)
followed by zero or more alphanumeric characters or the characters /, -, _ and .. In addition anything
enclosed in double quotes (") is recognized as a string.
String specification
# Interface name
filter input iifname eth0
# Weird interface name
filter input iifname "(eth0)"
LINK LAYER ADDRESS TYPE
┌────────────────────┬─────────┬──────────┬───────────┐
│ Name │ Keyword │ Size │ Base type │
├────────────────────┼─────────┼──────────┼───────────┤
│ Link layer address │ lladdr │ variable │ integer │
└────────────────────┴─────────┴──────────┴───────────┘
The link layer address type is used for link layer addresses. Link layer addresses are specified as a
variable amount of groups of two hexadecimal digits separated using colons (:).
Link layer address specification
# Ethernet destination MAC address
filter input ether daddr 20:c9:d0:43:12:d9
IPV4 ADDRESS TYPE
┌──────────────┬───────────┬────────┬───────────┐
│ Name │ Keyword │ Size │ Base type │
├──────────────┼───────────┼────────┼───────────┤
│ IPv4 address │ ipv4_addr │ 32 bit │ integer │
└──────────────┴───────────┴────────┴───────────┘
The IPv4 address type is used for IPv4 addresses. Addresses are specified in either dotted decimal, dot‐
ted 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}
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 ex‐
pressions 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 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 hardware │ iface_type │
│ │ type │ │
├───────────┼──────────────────────────────┼──────────────────┤
│ skuid │ UID associated with origi‐ │ uid │
│ │ nating socket │ │
├───────────┼──────────────────────────────┼──────────────────┤
│ skgid │ GID associated with origi‐ │ gid │
│ │ nating socket │ │
├───────────┼──────────────────────────────┼──────────────────┤
│ rtclassid │ Routing realm │ realm │
└───────────┴──────────────────────────────┴──────────────────┘
Meta expression specific types
┌─────────────┬───────────────────────────────────────┐
│ Type │ Description │
├─────────────┼───────────────────────────────────────┤
│ iface_index │ Interface index (32 bit number). Can │
│ │ be specified numerically or as name │
│ │ of an existing interface. │
├─────────────┼───────────────────────────────────────┤
│ ifname │ Interface name (16 byte string). Does │
│ │ not have to exist. │
├─────────────┼───────────────────────────────────────┤
│ iface_type │ Interface type (16 bit number). │
├─────────────┼───────────────────────────────────────┤
│ uid │ User ID (32 bit number). Can be spec‐ │
│ │ ified 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. │
└─────────────┴───────────────────────────────────────┘
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 Indicator │ flag │
├─────────┼────────────────────────────┼──────────────────┤
│ 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 │ FIXME │
├─────────┼──────────────────────┼─────────────────┤
│ ptype │ EtherType │ ethertype │
├─────────┼──────────────────────┼─────────────────┤
│ hlen │ Hardware address len │ integer (8 bit) │
├─────────┼──────────────────────┼─────────────────┤
│ plen │ Protocol address len │ integer (8 bit) │
├─────────┼──────────────────────┼─────────────────┤
│ op │ Operation │ FIXME │
└─────────┴──────────────────────┴─────────────────┘
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 including │ integer (4 bit) FIXME scal‐ │
│ │ options │ ing │
├───────────┼──────────────────────────────┼──────────────────────────────┤
│ tos │ Type Of Service │ FIXME │
├───────────┼──────────────────────────────┼──────────────────────────────┤
│ 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 │ │ │
├───────────┼───────────────────────┼──────────────────┤
│ flowlabel │ Flow label │ │
├───────────┼───────────────────────┼──────────────────┤
│ 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 scal‐ │
│ │ │ ing │
├──────────┼────────────────────────┼──────────────────────────────┤
│ reserved │ Reserved area │ FIXME │
├──────────┼────────────────────────┼──────────────────────────────┤
│ 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 │ FIXME │
├───────────┼──────────────────────────┼──────────────────┤
│ 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
ipcomp [IPComp header field]
IPComp header expression
┌─────────┬─────────────────────────────┬──────────────┐
│ Keyword │ Description │ Type │
├─────────┼─────────────────────────────┼──────────────┤
│ nexthdr │ Next header protocol │ inet_service │
├─────────┼─────────────────────────────┼──────────────┤
│ flags │ Flags │ FIXME │
├─────────┼─────────────────────────────┼──────────────┤
│ cfi │ Compression Parameter Index │ FIXME │
└─────────┴─────────────────────────────┴──────────────┘
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.
ct {state | direction | status | mark | expiration | helper | l3proto | saddr | daddr | protocol | proto-
src | proto-dst}
Conntrack expressions
┌────────────┬──────────────────────────────┬─────────────────────┐
│ Keyword │ Description │ Type │
├────────────┼──────────────────────────────┼─────────────────────┤
│ state │ State of the connection │ ct_state │
├────────────┼──────────────────────────────┼─────────────────────┤
│ direction │ Direction of the packet rel‐ │ ct_dir │
│ │ ative to the connection │ │
├────────────┼──────────────────────────────┼─────────────────────┤
│ status │ Status of the connection │ ct_status │
├────────────┼──────────────────────────────┼─────────────────────┤
│ mark │ Connection mark │ packetmark │
├────────────┼──────────────────────────────┼─────────────────────┤
│ expiration │ Connection expiration time │ time │
├────────────┼──────────────────────────────┼─────────────────────┤
│ helper │ Helper associated with the │ string │
│ │ connection │ │
├────────────┼──────────────────────────────┼─────────────────────┤
│ l3proto │ Layer 3 protocol of the con‐ │ nf_proto FIXME │
│ │ nection │ │
├────────────┼──────────────────────────────┼─────────────────────┤
│ saddr │ Source address of the con‐ │ ipv4_addr/ipv6_addr │
│ │ nection for the given direc‐ │ │
│ │ tion │ │
├────────────┼──────────────────────────────┼─────────────────────┤
│ daddr │ Destination address of the │ ipv4_addr/ipv6_addr │
│ │ connection for the given di‐ │ │
│ │ rection │ │
├────────────┼──────────────────────────────┼─────────────────────┤
│ protocol │ Layer 4 protocol of the con‐ │ inet_proto │
│ │ nection for the given direc‐ │ │
│ │ tion │ │
├────────────┼──────────────────────────────┼─────────────────────┤
│ proto-src │ Layer 4 protocol source for │ FIXME │
│ │ the given direction │ │
├────────────┼──────────────────────────────┼─────────────────────┤
│ proto-dst │ Layer 4 protocol destination │ FIXME │
│ │ for the given direction │ │
└────────────┴──────────────────────────────┴─────────────────────┘
STATEMENTS
Statements represent actions to be performed. They can alter control flow (return, jump to a different
chain, accept or drop the packet) or can perform actions, such as logging, rejecting a packet, etc.
Statements exist in two kinds. Terminal statements unconditionally terminate evaluation of the current
rule, non-terminal statements either only conditionally or never terminate evaluation of the current
rule, in other words, they are passive from the ruleset evaluation perspective. There can be an arbitrary
amount of non-terminal statements in a rule, but only a single terminal statement as the final statement.
VERDICT STATEMENT
The verdict statement alters control flow in the ruleset and issues policy decisions for packets.
{accept | drop | queue | continue | return}
{jump | goto} {chain}
accept 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 is‐
sued 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 re‐
turn 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 state‐
ment.
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 subsystem, related
to creation and deletion of objects. When they ocurr, nft will print to stdout the monitored events in
either XML, JSON or native nft format.
To filter events related to a concrete object, use one of the keywords 'tables', 'chains', 'sets',
'rules', 'elements'.
To filter events related to a concrete action, use keyword 'new' or 'destroy'.
Hit ^C to finish the monitor operation.
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 en‐
tire command is marked.
Error caused by single incorrect expression
<cmdline>:1:19-22: Error: Interface does not exist
filter output oif eth0
^^^^
Error caused by invalid combination of two expressions
<cmdline>:1:28-36: Error: Right hand side of relational expression (==) must be constant
filter output tcp dport == tcp dport
~~ ^^^^^^^^^
Error returned by the kernel
<cmdline>:0:0-23: Error: Could not process rule: Operation not permitted
filter output oif wlan0
^^^^^^^^^^^^^^^^^^^^^^^
EXIT STATUS
On success, nft exits with a status of 0. Unspecified errors cause it to exit with a status of 1, memory
allocation errors with a status of 2, unable to open Netlink socket with 3.
SEE ALSO
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@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-ShareAlike 4.0 li‐
cense, CC BY-SA 4.0 ⟨http://creativecommons.org/licenses/by-sa/4.0/⟩ .
06 November 2015 nft(8)