NAME

       skbmod - user-friendly packet editor action

SYNOPSIS

       tc ... action skbmod { [ set SETTABLE ] [ swap SWAPPABLE  ] [ 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.

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.  The  swap mac directive is performed after any outstanding D/SMAC
              changes.

       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 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

       Finally, swap the destination and source mac addresses in the 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

       As  mentioned  above, the swap action will occur after any  smac/dmac substitutions are executed, if they
       are present.

SEE ALSO

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