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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  Conges-
              tion  Encountered  (CE).  Does not affect Non ECN-Capable Trans-
              port (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  fil-
                     ter.
              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.   Try-
       ing  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)