If you suspect that firewall might be causing problems, your first instinct might be to use Wireshark to diagnose what the firewall is doing. However, this may be problematic, since WinPcap's behavior may differ greatly based on where the firewall and where WinPcap hook into the TCP/IP stack. (possible behaviors: 1) everything the firewall filters out may be visible in Wireshark, 2) it may be hidden from Wireshark, or 3) there might be a confusing mix)