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+.TH "ct action in tc" 8 "14 May 2020" "iproute2" "Linux"
+.SH NAME
+ct \- tc connection tracking action
+.SH SYNOPSIS
+.in +8
+.ti -8
+.BR "tc ... action ct commit [ force ] [ zone "
+.IR ZONE
+.BR "] [ mark "
+.IR MASKED_MARK
+.BR "] [ label "
+.IR MASKED_LABEL
+.BR "] [ nat "
+.IR NAT_SPEC
+.BR "]"
+
+.ti -8
+.BR "tc ... action ct [ nat ] [ zone "
+.IR ZONE
+.BR "]"
+
+.ti -8
+.BR "tc ... action ct clear"
+
+.SH 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.
+
+.SH OPTIONS
+.TP
+.BI zone " ZONE"
+Specify a conntrack zone number on which to send the packet to conntrack.
+.TP
+.BI mark " MASKED_MARK"
+Specify a masked 32bit mark to set for the connection (only valid with commit).
+.TP
+.BI label " MASKED_LABEL"
+Specify a masked 128bit label to set for the connection (only valid with commit).
+.TP
+.BI nat " NAT_SPEC"
+.BI 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).
+.RS
+.TP
+src/dst - configure src or dst nat
+.TP
+.BI  "" "addr1" "/" "addr2" " - IPv4/IPv6 addresses"
+.TP
+.BI  "" "port1" "/" "port2" " - Port numbers"
+.RE
+.TP
+.BI nat
+Restore any previous configured nat.
+.TP
+.BI clear
+Remove any conntrack state and metadata (mark/label) from the packet (must only option specified).
+.TP
+.BI force
+Forces conntrack direction for a previously committed connections, so that current direction will become the original direction (only valid with commit).
+
+.SH EXAMPLES
+Example showing natted firewall in conntrack zone 2, and conntrack mark usage:
+.EX
+
+#Add ingress qdisc on eth0 and eth1 interfaces
+.nf
+$ 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
+.fi
+
+.EE
+
+.RE
+.SH SEE ALSO
+.BR tc (8),
+.BR tc-flower (8)
+.BR tc-mirred (8)
+.SH AUTHORS
+Paul Blakey <paulb@mellanox.com>
+
+Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
+
+Yossi Kuperman <yossiku@mellanox.com>