ct action in tc

Section: Linux (8)
Updated: 14 May 2020
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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 handle ingress
$ tc qdisc add dev eth1 handle 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

AUTHORS

Paul Blakey <paulb@mellanox.com>

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

Yossi Kuperman <yossiku@mellanox.com>