LTM networking issue:

I am not familiar with FWSM, but I do have experience with a variety of other firewalls. Most firewalls will allow you to capture traffic on each individual interface. You just have to build the proper filter to capture the traffic you are looking for. Better yet, do the capture on the source and destination host. You can use wireshark, or microolap's tcpdump. Depending on how many nodes you have in the pool, it may be best to disable all but one, so you don't have to hunt for your session. Your src ip, src port, dst ip and dst port must match for the handshake to establish the session. If the SYN/ACK response does not match, the handshake will not establish.