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 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

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>

14 May 2020 iproute2