If you need to debug traffic going to a linux server or appliance, you can use tcpdump to generate a pcap file you can analyze in wireshark.
For example, ssh into the server, and use the following command:
tcpdump -s0 port 80 and host 192.168.1.10 -wDebugTraffic.pcap
This will capture all traffic coming into port 80 from host 192.168.1.10 and saved as file DebugTraffic.pcap
You can then use an ftp program (like WinSCP) to grab the file and analyze it in wireshark.
Here is a great resource for tcpdump commands: http://packetlife.net/media/library/12/tcpdump.pdf