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)