1skbmod action in tc(8)               Linux              skbmod action in tc(8)
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NAME

6       skbmod - user-friendly packet editor action
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SYNOPSIS

9       tc ... action skbmod { set SETTABLE | swap SWAPPABLE  | ecn } [ CONTROL
10               ] [ index INDEX ]
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12       SETTABLE :=  [ dmac DMAC ]  [ smac SMAC ]  [ etype ETYPE ]
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14       SWAPPABLE := mac
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16       CONTROL := { reclassify | pipe | drop | shot | continue | pass }
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DESCRIPTION

19       The skbmod action is intended as a usability upgrade  to  the  existing
20       pedit  action.  Instead  of  having to manually edit 8-, 16-, or 32-bit
21       chunks of an ethernet header, skbmod allows  complete  substitution  of
22       supported  elements.  Action must be one of set, swap and ecn.  set and
23       swap only affect Ethernet packets, while ecn only affects IP packets.
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OPTIONS

26       dmac DMAC
27              Change the destination mac to the specified address.
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29       smac SMAC
30              Change the source mac to the specified address.
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32       etype ETYPE
33              Change the ethertype to the specified value.
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35       mac    Used to swap mac addresses.
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37       ecn    Used to mark ECN Capable Transport (ECT) IP packets  as  Conges‐
38              tion  Encountered  (CE).  Does not affect Non ECN-Capable Trans‐
39              port (Non-ECT) packets.
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41       CONTROL
42              The following keywords allow one to  control  how  the  tree  of
43              qdisc,  classes,  filters and actions is further traversed after
44              this action.
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46              reclassify
47                     Restart with the first filter in the current list.
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49              pipe   Continue with the next action attached to the  same  fil‐
50                     ter.
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52              drop
53              shot   Drop the packet.
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55              continue
56                     Continue classification with the next filter in line.
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58              pass   Finish classification process and return to calling qdisc
59                     for further packet processing. This is the default.
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EXAMPLES

62       To start, observe the following filter with a pedit action:
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64              tc filter add dev eth1 parent 1: protocol ip prio 10 \
65                   u32 match ip protocol 1 0xff flowid 1:2 \
66                   action pedit munge offset -14 u8 set 0x02 \
67                   munge offset -13 u8 set 0x15 \
68                   munge offset -12 u8 set 0x15 \
69                   munge offset -11 u8 set 0x15 \
70                   munge offset -10 u16 set 0x1515 \
71                   pipe
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73       Using the skbmod action, this command can be simplified to:
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75              tc filter add dev eth1 parent 1: protocol ip prio 10 \
76                   u32 match ip protocol 1 0xff flowid 1:2 \
77                   action skbmod set dmac 02:15:15:15:15:15 \
78                   pipe
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80       Complexity will increase if source mac and  ethertype  are  also  being
81       edited  as  part  of  the action. If all three fields are to be changed
82       with skbmod:
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84              tc filter add dev eth5 parent 1: protocol ip prio 10 \
85                   u32 match ip protocol 1 0xff flowid 1:2 \
86                   action skbmod \
87                   set etype 0xBEEF \
88                   set dmac 02:12:13:14:15:16 \
89                   set smac 02:22:23:24:25:26
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91       To swap the destination  and  source  mac  addresses  in  the  Ethernet
92       header:
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94              tc filter add dev eth3 parent 1: protocol ip prio 10 \
95                   u32 match ip protocol 1 0xff flowid 1:2 \
96                   action skbmod \
97                   swap mac
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99       Finally,  to  mark  the  CE  codepoint in the IP header for ECN Capable
100       Transport (ECT) packets:
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102              tc filter add dev eth0 parent 1: protocol ip prio 10 \
103                   u32 match ip protocol 1 0xff flowid 1:2 \
104                   action skbmod \
105                   ecn
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107       Only one of set, swap and ecn shall be used in a single command.   Try‐
108       ing  to use more than one of them in a single command is considered un‐
109       defined behavior; pipe multiple commands together instead.
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SEE ALSO

113       tc(8), tc-u32(8), tc-pedit(8)
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117iproute2                          21 Sep 2016           skbmod action in tc(8)
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