Matching packet metainformation
The meta selectors allows you to match -- and in some cases, set -- packet metainformation. That is, information the local host has about the packet (such as how / when it was received) that is not necessarily carried in the packet itself.
Contents
Matching by packet info
The following meta selectors match packets by information carried by the packet itself:
meta Packet Info Selectors | ||||
---|---|---|---|---|
Keyword | Settable | Description | Data Type | Notes |
pkttype | Y | packet type | pkt_type | |
length | packet length in bytes | integer (32 bit) | ||
protocol | packet protocol / EtherType protocol value | ether_type | as in skb->protocol | |
nfproto | netfilter packet protocol family | integer (32 bit) | like ipv4, ipv6, etc...; useful only in inet table | |
l4proto | layer 4 protocol | integer (8 bit) | like tcp, udp, etc...; skips ipv6 extension headers |
Matching by interface
The following meta selectors match packets based on incoming or outgoing interfaces:
meta Interface Selectors | ||||
---|---|---|---|---|
Keyword | Settable | Description | Data Type | Notes |
iif | input interface index | iface_index | Faster than iifname as it only has to compare a 32-bit unsigned integer instead of a string.
The interface index is dynamically allocated, so don't use this for interfaces that are dynamically created and destroyed, eg. ppp0. | |
iifname | input interface name | ifname | ||
iiftype | input interface type | iface_type | ||
iifkind | input interface kind name | ifkind | ||
iifgroup | input interface group | devgroup | ||
oif | output interface index | iface_index | Faster than oifname as it only has to compare a 32-bit unsigned integer instead of a string.
The interface index is dynamically allocated, so don't use this for interfaces that are dynamically created and destroyed, eg. ppp0. | |
oifname | output interface name | ifname | ||
oiftype | output interface type | iface_type | ||
oifkind | output interface kind name | ifkind | ||
oifgroup | output interface group | devgroup | ||
ibrname | input bridge interface name | ifname | equivalent to obsolete ibriport keyword | |
obrname | output bridge interface name | ifname | equivalent to obsolete oibriport keyword | |
ibrvproto | input bridge vlan protocol | ether_type | ||
ibrpvid | input bridge port pvid | integer (16 bit) | ||
sdif | slave device interface index | integer | ||
sdifname | slave device interface name | ifname |
An example rule that uses iifname to accept all traffic entering the loopback pseudodevice lo:
% nft add rule filter input meta iifname lo accept
Matching by packet mark, routing class and realm
meta Packet Mark & Routing Selectors | ||||
---|---|---|---|---|
Keyword | Settable | Description | Data Type | Notes |
mark | Y | packet mark | mark | |
priority | Y | tc packet priority | tc_handle | detailed usage example |
rtclassid | routing realm | realm | Routing realm references: |
You can match packets whose mark is 123 with the following rule:
nft add rule filter output meta mark 123 counter
- Since nftables v0.7 you can match the packet priority, the tc classid:
% nft add rule filter forward meta priority abcd:1234
- Packet without set priority can be matched using meta priority none
% nft add rule filter forward meta priority none
See also: nexthop and fib selectors
Matching by socket UID / GID
meta UID / GID Selectors | ||||
---|---|---|---|---|
Keyword | Settable | Description | Data Type | Notes |
skuid | UID associated with originating socket | uid | ||
skgid | GID associated with originating socket | gid |
You can use your user name to match traffic, eg.
% nft add rule filter output meta skuid pablo counter
Or the 32-bits unsigned integer (UID) in case there is no entry in /etc/passwd for a given user.
% nft add rule filter output meta skuid 1000 counter
Let's just generate some HTTP traffic to test this rule:
% wget --spider http://www.google.com
Then, if you check the counters, you can verify that the packets are matching that rule.
% nft list table filter
table ip filter {
chain output {
type filter hook output priority 0;
skuid pablo counter packets 7 bytes 510
}
chain input {
type filter hook input priority 0;
}
}
Important: Beware if you test this with ping, it is usually installed with suid so that traffic will match the root user (uid=0).
Matching by time
meta Time Selectors | ||||
---|---|---|---|---|
Keyword | Settable | Description | Data Type | Notes |
time | timestamp of packet reception | time | Can specify as:
| |
day | day of week | day | Can specify as:
| |
hour | hour of day | hour | 24-hour "HH:MM:SS", with seconds optional. |
Matching by security selectors
meta Security Selectors | ||||
---|---|---|---|---|
Keyword | Settable | Description | Data Type | Notes |
cpu | CPU number processing the packet | integer (32 bit) | ||
cgroup | socket control group ID | integer (32 bit) | ||
secmark | Y | packet secmark | integer (32 bit) | |
ipsec | true if packet was ipsec encrypted | boolean (1 bit) | equivalent to obsolete secpath keyword |
Matching by miscellaneous selectors
In addition to those in the above subsections, the following miscellaneous meta selectors are available:
meta Miscellaneous Selectors | ||||
---|---|---|---|---|
Keyword | Settable | Description | Data Type | Notes |
nftrace | Y | nftrace debugging bit | boolean (1 bit) | |
random | pseudo-random number | integer (32 bit) |