Data types

From nftables wiki
Jump to: navigation, search

nft describe

You can use nft describe to get information about a data type, to find out the data type of a particular selector, and to list predefined symbolic constants for that selector. Some examples:

% nft describe iif
meta expression, datatype iface_index (network interface index) (basetype integer), 32 bits

% nft describe iifname
meta expression, datatype ifname (network interface name) (basetype string), 16 characters

% nft describe tcp flags
payload expression, datatype tcp_flag (TCP flag) (basetype bitmask, integer), 8 bits

pre-defined symbolic constants (in hexadecimal):
        fin                             0x01
        syn                             0x02
        rst                             0x04
        psh                             0x08
        ack                             0x10
        urg                             0x20
        ecn                             0x40
        cwr                             0x80


List of data types

Date and time types

Date and time types
Data Type Description Expressions Notes
day Day of week of packet reception (8 bit integer, with pre-defined symbolic constants):
  • Sunday
  • Monday
  • Tuesday
  • Wednesday
  • Thursday
  • Friday
  • Saturday
meta day Sunday = 0, Saturday = 6.

Symbolic constants are case insensitive, and unique abbreviations are accepted: Sun = sun = Sunday = 0.

hour Hour of day of packet reception (32 bit integer).

Specify as string in 24-hour format, hh:mm[:ss].

meta hour Seconds are optional: 17:00 = 17:00:00.
time Relative time of packet reception (64 bit integer). meta time Can be specified as a date in ISO format, i.e. "2019-06-06 17:00". Hour and seconds are optional and can be omitted if desired. If omitted, midnight will be assumed. The following three are equivalent: "2019-06-06" = "2019-06-06 00:00" = "2019-06-06 00:00:00".

When an integer is specified, it is assumed to be a UNIX timestamp.


Network interface types

Network interface types
Data Type Description Expressions Notes
devgroup Device group (32 bit integer). meta {iifgroup | oifgroup} Can be specified numerically or as symbolic name defined in /etc/iproute2/group.
iface_index Interface index (32 bit integer). meta {iif | oif} Can be specified numerically or as name of an existing interface.

Use ifname instead for interfaces whose name and/or index can change (i.e. those that appear / disappear dynamically).

iface_type Interface type (16 bit integer, with pre-defined symbolic constants):
  • ether
  • ppp
  • ipip
  • ipip6
  • loopback
  • sit
  • ipgre
meta {iiftype | oiftype}
ifkind Interface kind name (16 byte string). meta {iifkind | oifkind} dev->rtnl_link_ops->kind

The man 8 ip-link TYPES section lists valid ifkinds. It's missing at least one: tun.

ifname Interface name (16 byte string). meta {iifname | oifname} Does not have to exist.

Slower than iface_index but good for interfaces that can dynamically appear / disappear.


Ethernet types

Ethernet types
Data Type Description Expressions Notes
ether_addr Ethernet address (48 bit integer).
ether_type EtherType (16 bit integer, with pre-defined symbolic constants):
  • arp
  • ip
  • ip6
  • vlan
meta protocol ether.h has known types.

NOTE that ether.h lists EtherTypes in network order, while nft uses little-endian order on x86. (Check output of nft describe ether_type.)


ARP types

ARP types
Data Type Description Expressions Notes
ARP HLEN, hardware address length in octets (8 bit integer) arp hlen «HLEN» Unnamed 8-bit integer in nftables.

For ethernet HLEN = 6.

ARP HTYPE, hardware type (16 bit integer) arp htype «HTYPE» Unnamed 16-bit integer in nftables.

if_arp.h has known types.

ARP PLEN, internetwork address length in octets (8 bit integer) arp plen «PLEN» Unnamed 8-bit integer in nftables.

For IPv4 PLEN = 4.

arp_op ARP operation (16 bit integer, with pre-defined symbolic constants):
  • request = 1
  • reply = 2
  • rrequest = 3
  • rreply = 4
  • inrequest = 8
  • inreply = 9
  • nak = 10
arp operation «arp_op»


IP types

IP types
Data Type Description Expressions Notes
inet_proto Internet protocol (8 bit integer, with pre-defined symbolic constants):
  • tcp
  • udp
  • udplite
  • esp
  • ah
  • icmp
  • icmpv6
  • comp
  • dccp
  • sctp
in.h has known types.
inet_service Network service port number (16 bit integer).
ipv4_addr IPv4 address (32 bit integer).
ipv6_addr IPv6 address (128 bit integer).


Conntrack types

Conntrack types
Data Type Description Expressions Notes
ct_dir Conntrack direction (8 bit integer). Symbolic constants:
original       0
reply          1
ct_event Conntrack event bits (4 byte bitmask). Symbolic constants:
new            1
related        2
destroy        4
reply          8
assured       16
protoinfo     32
helper        64
mark         128
seqadj       256
secmark      512
label       1024
ct_label Conntrack label (128 bit bitmask).
ct_state Conntrack state (4 byte bitmask). Symbolic constants:
invalid        1
established    2
related        4
new            8
untracked     64
ct_status Conntrack status (4 byte bitmask). Symbolic constants:
expected       1
seen-reply     2
assured        4
confirmed      8
snat          16
dnat          32
dying        512


Other types

Other types
Data Type Description Expressions Notes
gid Group ID (32 bit integer). meta skgid Can be specified numerically or as group name.
mark Packet mark (32 bit integer).
pkt_type Packet type (8 bit integer, with pre-defined symbolic constants):
  • host or unicast - addressed to local host
  • broadcast - to all
  • multicast - to group
  • other - addressed to another host
meta pkttype
realm Routing Realm (32 bit integer). meta rtclassid Can be specified numerically or as symbolic name defined in /etc/iproute2/rt_realms.

Routing realm references:

uid User ID (32 bit integer). meta skuid Can be specified numerically or as user name.