how do you do GTP dynamic IP capture filtering?

Hi,

I am trying to do GTP capture filtering because of the amount of traffic on the server, last time I was told to use the following filtering:

(vlan and ip6[64:4]=0x2a008a00 and ip6[68:4]=0x20000035 and ip6[72:4]=0x00000000 and ip6[76:4]=0x00000011)

the problem is that the SIP messages' header are not always at the same position due to different messages, is there another way to capture them?

Thanks! Joseph