Manual: tc-skbmod

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 Congestion Encountered (CE).  Does not affect Non	ECN-
	      Capable Transport (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 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

       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)