tc-fw(8) — Linux manual page

Firewall mark classifier in tc(8) Linux Firewall mark classifier in tc(8)

NAME         top

       fw - fwmark traffic control filter

SYNOPSIS         top

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

DESCRIPTION         top

       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         top

       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         top

       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         top

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

COLOPHON         top

       This page is part of the iproute2 (utilities for controlling
       TCP/IP networking and traffic) project.  Information about the
       project can be found at 
       ⟨http://www.linuxfoundation.org/collaborate/workgroups/networking/iproute2⟩.
       If you have a bug report for this manual page, send it to
       netdev@vger.kernel.org, shemminger@osdl.org.  This page was
       obtained from the project's upstream Git repository
       ⟨https://git.kernel.org/pub/scm/network/iproute2/iproute2.git⟩ on
       2025-08-11.  (At that time, the date of the most recent commit
       that was found in the repository was 2025-08-08.)  If you discover
       any rendering problems in this HTML version of the page, or you
       believe there is a better or more up-to-date source for the page,
       or you have corrections or improvements to the information in this
       COLOPHON (which is not part of the original manual page), send a
       mail to man-pages@man7.org

iproute2                       21 Oct 201F5irewall mark classifier in tc(8)

Pages that refer to this page: tc(8)

HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH.