Hi,
this is my first post to this list.
I try to match several RTPv2 codecs with tc u32 and I ended up with the following:
tc filter add dev mydevice protocol ip parent 1:0 pref 3 u32 \
match ip protocol 0x11 0xFF \
match u16 0x8008 0xC07F at 28 \
flowid 1:110
So far this works. It means (at least I hope so):
- match UDP,
- match the first two bytes in the UDP payload, which are part of the RTP header
- first two bits say „version 2“ RTP
- last 7 bits encode the codec. In this example G.711 PCMA
So now this code is just working for IPv4. And I would like to have a more generic one using nexthdr. So I tried:
tc filter add dev mydevice protocol ip parent 1:0 pref 3 u32 \
match ip protocol 0x11 0xFF \
match u16 0x8008 0xC07F at nexthdr+4 \
flowid 1:110
Problem with this is that it matches packets, but when doing a test call with VoIP I can see that it does not match RTP traffic but some wrong traffic. So I guess my „nexthdr+4“ is wrong. I thought that the nexthdr depends on the selector u16 and therefor needs to be 4. 4*16=64, which should be 8 bytes offset to UDP, which is the beginning of the payload, isn’t it?
Can someone help me fixing this rule? Thanks in advance
Kind regards
-Christian Rößner
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