tcpdump
Linux Commands - Administrative Commands

tcpdump

This is a useful debugging tool. Example: tcpdump host somesite.com and anothersite.com This will return output communication between the two domains. tcpdump port ftp This will show problems you may be having connecting to a ftp server. You may have to use port ftp-data for the data transfer as well. tcpdump port 80 This will allow you to see the http communications.