"skbmod action in tc" 8 "21 Sep 2016" "iproute2" "Linux"


 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 .TQ
 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:



.EX
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:



.EX
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:



.EX
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:



.EX
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)