# tc-ct

## 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 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
    


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