tc-ct8

Usage

Overview

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