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  ] [ 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)

iproute2                                                            21 Sep 2016                                             skbmod action in tc(8)