tc-skbmod(8) — Linux manual page

skbmod action in tc(8)            Linux           skbmod action in tc(8)

NAME

       skbmod - user-friendly packet editor action

SYNOPSIS

       tc ... action skbmod { set SETTABLE | swap SWAPPABLE  | ecn } [
               CONTROL ] [ index INDEX ]

       SETTABLE :=  [ dmac DMAC ]  [ smac SMAC ]  [ etype ETYPE ]

       SWAPPABLE := mac

       CONTROL := { reclassify | pipe | drop | shot | continue | pass }

DESCRIPTION

       The skbmod action is intended as a usability upgrade to the
       existing pedit action. Instead of having to manually edit 8-,
       16-, or 32-bit chunks of an ethernet header, skbmod allows
       complete substitution of supported elements.  Action must be one
       of set, swap and ecn.  set and swap only affect Ethernet packets,
       while ecn only affects IP packets.

OPTIONS

       dmac DMAC
              Change the destination mac to the specified address.

       smac SMAC
              Change the source mac to the specified address.

       etype ETYPE
              Change the ethertype to the specified value.

       mac    Used to swap mac addresses.

       ecn    Used to mark ECN Capable Transport (ECT) IP packets as
              Congestion Encountered (CE).  Does not affect Non ECN-
              Capable Transport (Non-ECT) packets.

       CONTROL
              The following keywords allow one to control how the tree
              of qdisc, classes, filters and actions is further
              traversed after this action.

              reclassify
                     Restart with the first filter in the current list.

              pipe   Continue with the next action attached to the same
                     filter.

              drop
              shot   Drop the packet.

              continue
                     Continue classification with the next filter in
                     line.

              pass   Finish classification process and return to calling
                     qdisc for further packet processing. This is the
                     default.

EXAMPLES

       To start, observe the following filter with a pedit action:

              tc filter add dev eth1 parent 1: protocol ip prio 10 \
                   u32 match ip protocol 1 0xff flowid 1:2 \
                   action pedit munge offset -14 u8 set 0x02 \
                   munge offset -13 u8 set 0x15 \
                   munge offset -12 u8 set 0x15 \
                   munge offset -11 u8 set 0x15 \
                   munge offset -10 u16 set 0x1515 \
                   pipe

       Using the skbmod action, this command can be simplified to:

              tc filter add dev eth1 parent 1: protocol ip prio 10 \
                   u32 match ip protocol 1 0xff flowid 1:2 \
                   action skbmod set dmac 02:15:15:15:15:15 \
                   pipe

       Complexity will increase if source mac and ethertype are also
       being edited as part of the action. If all three fields are to be
       changed with skbmod:

              tc filter add dev eth5 parent 1: protocol ip prio 10 \
                   u32 match ip protocol 1 0xff flowid 1:2 \
                   action skbmod \
                   set etype 0xBEEF \
                   set dmac 02:12:13:14:15:16 \
                   set smac 02:22:23:24:25:26

       To swap the destination and source mac addresses in the Ethernet
       header:

              tc filter add dev eth3 parent 1: protocol ip prio 10 \
                   u32 match ip protocol 1 0xff flowid 1:2 \
                   action skbmod \
                   swap mac

       Finally, to mark the CE codepoint in the IP header for ECN
       Capable Transport (ECT) packets:

              tc filter add dev eth0 parent 1: protocol ip prio 10 \
                   u32 match ip protocol 1 0xff flowid 1:2 \
                   action skbmod \
                   ecn

       Only one of set, swap and ecn shall be used in a single command.
       Trying to use more than one of them in a single command is
       considered undefined behavior; pipe multiple commands together
       instead.

SEE ALSO

       tc(8), tc-u32(8), tc-pedit(8)

COLOPHON

       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
       2024-06-14.  (At that time, the date of the most recent commit
       that was found in the repository was 2024-06-11.)  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 Sep 2016        skbmod action in tc(8)

Pages that refer to this page: tc-actions(8)

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