[Joan <aseques@xxxxxxxxx>]

I am trying to extract the data transmitted into a l2tp tunnel, I am running thsark/tcpdump in the tunnel terminator. What I am using so far is this (4291 is the tunnel number):

  tcpdump -n -i eth3.800 "udp port 1701 && udp[8:2] & 0x80ff == 0x0002 && udp[10:2] == 4291" 

I took the filter line from here http://networkingbodges.blogspot.com.es/2012/11/tshark-one-liners.html

The problem is that I would like to inspect the traffic inside the tunnel, but I could'nt find a reference on this.

Any clues?