Matching packet metainformation: Difference between revisions

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The meta selectors allows you to match -- [[Setting_packet_metainformation |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.
The meta selectors allows you to match -- [[Setting_packet_metainformation |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.


= Miscellaneous meta selectors =
= Matching by packet info =


In addition to the meta selectors in the following subsections, the following meta selectors are available:
The following ''meta'' selectors match packets by information carried by the packet itself:


{| class="wikitable"
{| class="wikitable"
!colspan="5"|''meta'' Selectors
!colspan="5"|''meta'' Packet Info Selectors
|- style="vertical-align:bottom;"
|- style="vertical-align:bottom;"
! Keyword
! Keyword
Line 13: Line 13:
! style="text-align:left;" | [[Data_types|Data Type]]
! style="text-align:left;" | [[Data_types|Data Type]]
! style="text-align:left;" | Notes
! style="text-align:left;" | Notes
|- style="vertical-align:top;"
| ''mark''
| [[Setting_packet_metainformation |Y]]
| packet mark
| mark
|
|- style="vertical-align:top;"
| ''skuid''
|
| UID associated with originating socket
| uid
|
|- style="vertical-align:top;"
| ''skgid''
|
| GID associated with originating socket
| gid
|
|- style="vertical-align:top;"
| ''nftrace''
| [[Setting_packet_metainformation |Y]]
| [[Ruleset_debug/tracing|nftrace debugging]] bit
|
|
|- style="vertical-align:top;"
| ''rtclassid''
|
| routing realm
| realm
|
|- style="vertical-align:top;"
| ''ibriport''
|
| input bridge port
|
|
|- style="vertical-align:top;"
| ''obriport''
|
| output bridge port
|
|
|- style="vertical-align:top;"
| ''ibrname''
|
| input bridge interface name
| ifname
|
|- style="vertical-align:top;"
| ''obrname''
|
| output bridge interface name
| ifname
|


|- style="vertical-align:top;"
|- style="vertical-align:top;"
| ''pkttype''
| ''pkttype''
| [[Setting_packet_metainformation |Y]]
| [[Setting_packet_metainformation |Y]]
| packet type
| packet type (''unicast'', ''broadcast'', ''multicast'', ''other'')
| pkt_type
| pkt_type
|
|- style="vertical-align:top;"
| ''cpu''
|
| CPU number processing the packet
| integer (32 bit)
|
|- style="vertical-align:top;"
| ''cgroup''
|
| control group ID
| integer (32 bit)
|
|- style="vertical-align:top;"
| ''ipsec''
|
| true if packet was ipsec encrypted
| boolean (1 bit)
|
|- style="vertical-align:top;"
| ''time''
|
| timestamp of packet reception
| integer (32 bit) or string
|
|- style="vertical-align:top;"
| ''day''
|
| day of week
| integer (32 bit) or string
|
|- style="vertical-align:top;"
| ''hour''
|
| hour of day
| string
|
|


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| integer (8 bit)
| integer (8 bit)
| like tcp, udp, etc...; skips ipv6 extension headers
| like tcp, udp, etc...; skips ipv6 extension headers
|- style="vertical-align:top;"
| ''priority''
| [[Setting_packet_metainformation |Y]]
| tc packet priority
| tc_handle
|
|- style="vertical-align:top;"
| ''random''
|
| pseudo-random number
| integer (32 bit)
|
|- style="vertical-align:top;"
| ''secmark''
| [[Setting_packet_metainformation |Y]]
| packet secmark
|
|
|- style="vertical-align:top;"
| ''ibrvproto''
|
| bridge protocol
|
|
|- style="vertical-align:top;"
| ''ibrpvid''
|
| bridge pvid
|
|


|}
|}
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= Matching by interface =
= Matching by interface =


The following meta selectors match packets based on incoming or outgoing interfaces:
The following ''meta'' selectors match packets based on incoming or outgoing interfaces:


{| class="wikitable"
{| class="wikitable"
Line 220: Line 80:


|- style="vertical-align:top;"
|- style="vertical-align:top;"
| ''iifgroup''
| ''iiftype''
|
| input interface type
| iface_type
|
 
|- style="vertical-align:top;"
| ''iifkind''
|
|
| input interface group
| input interface kind name
| devgroup
| ifkind
|
|


|- style="vertical-align:top;"
|- style="vertical-align:top;"
| ''iiftype''
| ''iifgroup''
|
|
| input interface type
| input interface group
| iface_type
| devgroup
|
|


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| output interface name
| output interface name
| ifname
| ifname
|
|- style="vertical-align:top;"
| ''oiftype''
|
| output interface type
| iface_type
|
|- style="vertical-align:top;"
| ''oifkind''
|
| output interface kind name
| ifkind
|
|


Line 256: Line 137:


|- style="vertical-align:top;"
|- style="vertical-align:top;"
| ''oiftype''
| ''ibrname''
|
| input bridge interface name
| ifname
| equivalent to obsolete ''ibriport'' keyword
 
|- style="vertical-align:top;"
| ''obrname''
|
| output bridge interface name
| ifname
|equivalent to obsolete ''oibriport'' keyword
 
|- style="vertical-align:top;"
| ''ibrvproto''
|
| input bridge vlan protocol
| ether_type
|
 
|- style="vertical-align:top;"
| ''ibrpvid''
|
|
| output interface type
| input bridge port pvid
| iface_type
| integer (16 bit)
|
 
|- style="vertical-align:top;"
| ''sdif''
|
| slave device interface index
| integer
|
 
|- style="vertical-align:top;"
| ''sdifname''
|
|
| slave device interface name
| ifname
|


|}
|}
Line 270: Line 186:
</source>
</source>


= Matching by packet mark =
= Matching by packet mark, routing class and realm =
 
{| class="wikitable"
!colspan="5"|''meta'' Packet Mark & Routing Selectors
|- style="vertical-align:bottom;"
! Keyword
! [[Setting_packet_metainformation |Settable]]
! style="text-align:left;" | Description
! style="text-align:left;" | [[Data_types|Data Type]]
! style="text-align:left;" | Notes
 
|- style="vertical-align:top;"
| ''mark''
| [[Setting_packet_metainformation |Y]]
| packet mark
| mark
|
 
|- style="vertical-align:top;"
| ''priority''
| [[Setting_packet_metainformation |Y]]
| tc packet priority
| tc_handle
| [[Classification_to_tc_structure_example |detailed usage example]]
 
|- style="vertical-align:top;"
| ''rtclassid''
|
| routing realm
| realm
| Routing realm references:
<ul>
<li>[http://linux-ip.net/gl/ip-cref/ip-cref-node172.html linux-ip.net]
<li>[http://www.policyrouting.org/PolicyRoutingBook/ONLINE/CH07.web.html policyrouting.org]
</ul>
 
|}


You can match packets whose mark is 123 with the following rule:
You can match packets whose mark is 123 with the following rule:
Line 278: Line 230:
</source>
</source>


= Matching by socket UID =
* Since nftables v0.7 you can match the packet priority, the tc classid:
 
<source>
% nft add rule filter forward meta priority abcd:1234
</source>
 
* Packet without set priority can be matched using meta priority none
<source>
% nft add rule filter forward meta priority none
</source>
 
See also: [[Matching routing information|''nexthop'' and ''fib'' selectors]]
 
 
= Matching by socket UID / GID =
 
{| class="wikitable"
!colspan="5"|''meta'' UID / GID Selectors
|- style="vertical-align:bottom;"
! Keyword
! [[Setting_packet_metainformation |Settable]]
! style="text-align:left;" | Description
! style="text-align:left;" | [[Data_types|Data Type]]
! style="text-align:left;" | Notes
 
|- style="vertical-align:top;"
| ''skuid''
|
| UID associated with originating socket
| uid
|
 
|- style="vertical-align:top;"
| ''skgid''
|
| GID associated with originating socket
| gid
|
 
|}


You can use your user name to match traffic, eg.
You can use your user name to match traffic, eg.
Line 316: Line 307:
'''Important''': Beware if you test this with ''ping'', it is usually installed with suid so that traffic will match the root user (uid=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 tc priority =


* Since nftables v0.7 you can match the packet priority, the tc classid:
= Matching by time =
 
{| class="wikitable"
!colspan="5"|''meta'' Time Selectors
|- style="vertical-align:bottom;"
! Keyword
! [[Setting_packet_metainformation |Settable]]
! style="text-align:left;" | Description
! style="text-align:left;" | [[Data_types|Data Type]]
! style="text-align:left;" | Notes
 
|- style="vertical-align:top;"
| ''time''
|
| timestamp of packet reception
| time
| Can specify as:
* integer: ns since epoch, or
* string: date in ISO format.
 
|- style="vertical-align:top;"
| ''day''
|
| day of week
| day
| Can specify as:
* integer: 0 = Sunday to 6 = Saturday, or
* case-insensitive string: "Monday", "tuesday", etc. Unique abbreviations also work: "fri", "Sat".
 
|- style="vertical-align:top;"
| ''hour''
|
| hour of day
| hour
| 24-hour "HH:MM:SS", with seconds optional.
 
|}
 
 
= Matching by security selectors =
 
{| class="wikitable"
!colspan="5"|''meta'' Security Selectors
|- style="vertical-align:bottom;"
! Keyword
! [[Setting_packet_metainformation |Settable]]
! style="text-align:left;" | Description
! style="text-align:left;" | [[Data_types|Data Type]]
! style="text-align:left;" | Notes
 
|- style="vertical-align:top;"
| ''cpu''
|
| CPU number processing the packet
| integer (32 bit)
|
 
|- style="vertical-align:top;"
| ''cgroup''
|
| socket control group ID
| integer (32 bit)
|
 
|- style="vertical-align:top;"
| ''secmark''
| [[Setting_packet_metainformation |Y]]
| packet secmark
| integer (32 bit)
|
 
|- style="vertical-align:top;"
| ''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:
 
{| class="wikitable"
!colspan="5"|''meta'' Miscellaneous Selectors
|- style="vertical-align:bottom;"
! Keyword
! [[Setting_packet_metainformation |Settable]]
! style="text-align:left;" | Description
! style="text-align:left;" | [[Data_types|Data Type]]
! style="text-align:left;" | Notes
 
|- style="vertical-align:top;"
| ''nftrace''
| [[Setting_packet_metainformation |Y]]
| [[Ruleset_debug/tracing|nftrace debugging]] bit
| boolean (1 bit)
|


<source>
|- style="vertical-align:top;"
% nft add rule filter forward meta priority abcd:1234
| ''random''
</source>
|
| pseudo-random number
| integer (32 bit)
|


* Packet without set priority can be matched using meta priority none
|}
<source>
% nft add rule filter forward meta priority none
</source>

Latest revision as of 15:33, 28 March 2024

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.

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 (unicast, broadcast, multicast, other) 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:
  • integer: ns since epoch, or
  • string: date in ISO format.
day day of week day Can specify as:
  • integer: 0 = Sunday to 6 = Saturday, or
  • case-insensitive string: "Monday", "tuesday", etc. Unique abbreviations also work: "fri", "Sat".
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)