Name
ct - tc connection tracking actionSynopsis
"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
Specify a conntrack zone number on which to send the packet to conntrack.
Specify a masked 32bit mark to set for the connection (only valid with commit).
Specify a masked 128bit label to set for the connection (only valid with commit).
Specify src/dst and range of nat to configure for the connection (only valid with commit).
src/dst - configure src or dst nat
Restore any previous configured nat.
Remove any conntrack state and metadata (mark/label) from the packet (must only option specified).
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