Anyone who works with computer networks often needs a protocol analyzer to help understand what's happening on the network. One I have often used in my work is called "Wireshark" (formerly Ethereal). With Wireshark, you can examine the various protocols, examine addresses, follow TCP/IP streams and much more. It's available for Linux, Windows and Mac. I have used both the Linux and Windows versions for many years. It can be downloaded for free from the Wireshark web site. It's also included with many Linux distros. It's a valuable tool for anyone involved with computer networking.