Wireshark is a network packet analyzer. A network packet analyzer will try to capture network packets and tries to display that packet data as detailed as possible.

You could think of a network packet analyzer as a measuring device used to examine what's going on inside a network cable, just like a voltmeter is used by an electrician to examine what's going on inside an electric cable (but at a higher level, of course).

In the past, such tools were either very expensive, proprietary, or both. However, with the advent of Wireshark, all that has changed.

Wireshark is perhaps one of the best open source packet analyzers available today.

Examples:

network administrators use it to troubleshoot network problems

network security engineers use it to examine security problems

developers use it to debug protocol implementations

people use it to learn network protocol internals

Beside these examples, Wireshark can be helpful in many other situations too.

Features:

The following are some of the many features Wireshark provides:

Available for UNIX and Windows.

Capture live packet data from a network interface.

Display packets with very detailed protocol information.

Open and Save packet data captured.

Import and Export packet data from and to a lot of other capture programs.

Filter packets on many criteria.

Search for packets on many criteria.

Colorize packet display based on filters.

Create various statistics.

... and a lot more!