ct action in tc(8) Linux ct action in tc(8)

# [NAME](#NAME)

ct - tc connection tracking action

# [SYNOPSIS](#SYNOPSIS)

**tc ... action ct commit \[ force ] \[ zone** *ZONE* **] \[ mark** *MASKED\_MARK* **] \[ label** *MASKED\_LABEL* **] \[ nat** *NAT\_SPEC* **]**

**tc ... action ct \[ nat ] \[ zone** *ZONE* **]**

**tc ... action ct clear**

# [DESCRIPTION](#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.

# [OPTIONS](#OPTIONS)

[**zone ZONE**](#zone)

Specify a conntrack zone number on which to send the packet to conntrack.

[**mark MASKED\_MARK**](#mark)

Specify a masked 32bit mark to set for the connection (only valid with commit).

[**label MASKED\_LABEL**](#label)

Specify a masked 128bit label to set for the connection (only valid with commit).

[**nat NAT\_SPEC**](#nat)

**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).

[src/dst - configure src or dst nat](#src/dst)

**addr1/addr2 - IPv4/IPv6 addresses**

**port1/port2 - Port numbers**

[**nat**](#nat~2)

Restore any previous configured nat.

[**clear**](#clear)

Remove any conntrack state and metadata (mark/label) from the packet (must only option specified).

[**force**](#force)

Forces conntrack direction for a previously committed connections, so that current direction will become the original direction (only valid with commit).

# [EXAMPLES](#EXAMPLES)

Example showing natted firewall in conntrack zone 2, and conntrack mark usage:

```
#Add ingress qdisc on eth0 and eth1 interfaces


$ 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
```

# [SEE ALSO](#SEE_ALSO)

[**tc**(8)](/man/os/iproute2/tc.8), [**tc-flower**(8)](/man/os/iproute2/tc-flower.8) [**tc-mirred**(8)](/man/os/iproute2/tc-mirred.8)

# [AUTHORS](#AUTHORS)

Paul Blakey <paulb@mellanox.com>

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

Yossi Kuperman <yossiku@mellanox.com>

14 May 2020 iproute2

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Document: tc-ct(8) from iproute2 7.2.0-r0 (Chainguard OS)
Source: https://kernel.googlesource.com/pub/scm/network/iproute2/iproute2