Linux cli command tc-ct

➡ A Linux man page (short for manual page) is a form of software documentation found on Linux and Unix-like operating systems. This man-page explains the command tc-ct and provides detailed information about the command tc-ct, system calls, library functions, and other aspects of the system, including usage, options, and examples of _. You can access this man page by typing man followed by the tc-ct.

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NAME 🖥️ tc-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-flower(8) tc-mirred(8)

AUTHORS

Paul Blakey <[email protected]>

Marcelo Ricardo Leitner <[email protected]>

Yossi Kuperman <[email protected]>

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