phpman > man > tc-skbmod(8)

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  com‐
       plete  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 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 ac‐
       tion. 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)



iproute2                                     21 Sep 2016                      skbmod action in tc(8)