How to see a tunnel traffic with tcpdump or another tool ?

Hi I was wondering if it is possible to look in to an APM (PPP) tunnel using for Network Access. Can tcpdump or some other tool use to watch/monitor APM tunnels ?

 

When I use the tcpdump with IP address of the client which is connected with a Network Access VPN tunnel on F5, I can easily see the packets that coming from client computer. But the tcpdump accepts that IP address as a filter and it only shows unicast traffic. I would like to see multicast and broadcast traffics that generated by clients.