NAME

       fw - fwmark traffic control filter

SYNOPSIS

       tc filter ... fw [ classid CLASSID ] [ action ACTION_SPEC ]

DESCRIPTION

       the fw filter allows one to classify packets based on a previously set fwmark by iptables.  If the masked
       value  of  the  fwmark matches the filter's masked handle, the filter matches. By default, all 32 bits of
       the handle and the fwmark are masked.  iptables allows one to mark single packets with the  MARK  target,
       or whole connections using CONNMARK.  The benefit of using this filter instead of doing the heavy-lifting
       with  tc itself is that on one hand it might be convenient to keep packet filtering and classification in
       one place, possibly having to match a packet just once, and on the other users familiar with iptables but
       not tc will have a less hard time adding QoS to their setups.

OPTIONS

       classid CLASSID
              Push matching packets to the class identified by CLASSID.

       action ACTION_SPEC
              Apply an action from the generic actions framework on matching packets.

EXAMPLES

       Take e.g. the following tc filter statement:

              tc filter add ... handle 6 fw classid 1:1

       will match if the packet's fwmark value is 6.  This is a sample iptables statement marking packets coming
       in on eth0:

              iptables -t mangle -A PREROUTING -i eth0 -j MARK --set-mark 6

       Specific bits of the packet's fwmark can be set using the skbedit action. For example, to  only  set  one
       bit of the fwmark without changing any other bit:

              tc filter add ... action skbedit mark 0x8/0x8

       The fw filter can then be used to match on this bit by masking the handle:

              tc filter add ... handle 0x8/0x8 fw action drop

       This is useful when different bits of the fwmark are assigned different meanings.

SEE ALSO

       tc(8), iptables(8), iptables-extensions(8), tc-skbedit(8)

iproute2                                           21 Oct 2015                 Firewall mark classifier in tc(8)