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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXAMPLES | SEE ALSO | AUTHORS | COLOPHON |
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ct action in tc(8) Linux ct action in tc(8)
ct - tc connection tracking action
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
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.
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).
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
tc(8), tc-flower(8) tc-mirred(8)
Paul Blakey <paulb@mellanox.com>
Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Yossi Kuperman <yossiku@mellanox.com>
This page is part of the iproute2 (utilities for controlling
TCP/IP networking and traffic) project. Information about the
project can be found at
⟨http://www.linuxfoundation.org/collaborate/workgroups/networking/iproute2⟩.
If you have a bug report for this manual page, send it to
netdev@vger.kernel.org, shemminger@osdl.org. This page was
obtained from the project's upstream Git repository
⟨https://git.kernel.org/pub/scm/network/iproute2/iproute2.git⟩ on
2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-08-08.) If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page,
or you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a
mail to man-pages@man7.org
iproute2 14 May 2020 ct action in tc(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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