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ct action in tc(8) Linux ct action in tc(8)
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 con-
ntrack 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 op-
tion 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
SEE ALSO
tc(8), tc-flower(8) tc-mirred(8)
AUTHORS
Paul Blakey <paulb AT mellanox.com>
Marcelo Ricardo Leitner <marcelo.leitner AT gmail.com>
Yossi Kuperman <yossiku AT mellanox.com>
iproute2 14 May 2020 ct action in tc(8)
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