.TH "ct action in tc" 8 "14 May 2020" "iproute2" "Linux"
.SH NAME
ct \- tc connection tracking action
.SH SYNOPSIS
.in +8
.ti -8
.BR "tc ... action ct commit [ force ] [ zone "
.IR ZONE
.BR "] [ mark "
.IR MASKED_MARK
.BR "] [ label "
.IR MASKED_LABEL
.BR "] [ nat "
.IR NAT_SPEC
.BR "]"

.ti -8
.BR "tc ... action ct [ nat ] [ zone "
.IR ZONE
.BR "]"

.ti -8
.BR "tc ... action ct clear"

.SH DESCRIPTION
The ct action is a tc action for sending packets and interacting with the netfilter conntrack module.

It can (as shown in the synopsis, in order):

Send the packet to conntrack, and commit the connection, while configuring
a 32bit mark, 128bit label, and src/dst nat.

Send the packet to conntrack, which will mark the packet with the connection's state and
configured metadata (mark/label), and execute previous configured nat.

Clear the packet's of previous connection tracking state.

.SH OPTIONS
.TP
.BI zone " ZONE"
Specify a conntrack zone number on which to send the packet to conntrack.
.TP
.BI mark " MASKED_MARK"
Specify a masked 32bit mark to set for the connection (only valid with commit).
.TP
.BI label " MASKED_LABEL"
Specify a masked 128bit label to set for the connection (only valid with commit).
.TP
.BI nat " NAT_SPEC"
.BI Where " NAT_SPEC " ":= {src|dst} addr" " addr1" "[-" "addr2" "] [port " "port1" "[-" "port2" "]]"

Specify src/dst and range of nat to configure for the connection (only valid with commit).
.RS
.TP
src/dst - configure src or dst nat
.TP
.BI  "" "addr1" "/" "addr2" " - IPv4/IPv6 addresses"
.TP
.BI  "" "port1" "/" "port2" " - Port numbers"
.RE
.TP
.BI nat
Restore any previous configured nat.
.TP
.BI clear
Remove any conntrack state and metadata (mark/label) from the packet (must only option specified).
.TP
.BI force
Forces conntrack direction for a previously committed connections, so that current direction will become the original direction (only valid with commit).

.SH EXAMPLES
Example showing natted firewall in conntrack zone 2, and conntrack mark usage:
.EX

#Add ingress qdisc on eth0 and eth1 interfaces
.nf
$ tc qdisc add dev eth0 ingress
$ tc qdisc add dev eth1 ingress

#Setup filters on eth0, allowing opening new connections in zone 2, and doing src nat + mark for each new connection
$ tc filter add dev eth0 ingress prio 1 chain 0 proto ip flower ip_proto tcp ct_state -trk \\
action ct zone 2 pipe action goto chain 2
$ tc filter add dev eth0 ingress prio 1 chain 2 proto ip flower ct_state +trk+new \\
action ct zone 2 commit mark 0xbb nat src addr 5.5.5.7 pipe action mirred egress redirect dev eth1
$ tc filter add dev eth0 ingress prio 1 chain 2 proto ip flower ct_zone 2 ct_mark 0xbb ct_state +trk+est \\
action ct nat pipe action mirred egress redirect dev eth1

#Setup filters on eth1, allowing only established connections of zone 2 through, and reverse nat (dst nat in this case)
$ tc filter add dev eth1 ingress prio 1 chain 0 proto ip flower ip_proto tcp ct_state -trk \\
action ct zone 2 pipe action goto chain 1
$ tc filter add dev eth1 ingress prio 1 chain 1 proto ip flower ct_zone 2 ct_mark 0xbb ct_state +trk+est \\
action ct nat pipe action mirred egress redirect dev eth0
.fi

.EE

.RE
.SH SEE ALSO
.BR tc (8),
.BR tc-flower (8)
.BR tc-mirred (8)
.SH AUTHORS
Paul Blakey <paulb@mellanox.com>

Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>

Yossi Kuperman <yossiku@mellanox.com>