---
name: "tc-ct"
section: "8"
platform: "linux"
package: "iproute2"
version: "7.3.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/tc-ct"
---

# tc-ct(8)

tc connection tracking action

## NAME

ct - tc connection tracking action

## 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

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

- **zone** *ZONE*

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

- **mark** *MASKED\_MARK*

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

- **label** *MASKED\_LABEL*

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

- **nat** *NAT\_SPEC*

  **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

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

    - *port1***/***port2* **- Port numbers**

    - **nat**

  Restore any previous configured nat.

- **clear**

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

- **force**

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

## 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

[**tc**(8)](/tc/8.md), [**tc-flower**(8)](/tc-flower/8.md) [**tc-mirred**(8)](/tc-mirred/8.md)

## AUTHORS

Paul Blakey \<paulb@mellanox.com\>

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

Yossi Kuperman \<yossiku@mellanox.com\>