Wireless Hacks

Visual Traffic Analysis with Ethereal

Sift through network data with one of the most advanced protocol analyzers available.

Ethereal is one of the most popular protocol analyzers on the planet. It runs on virtually all major platforms, including Linux, BSD, Mac OS X, and Windows. Like tcpdump [Hack #37], it can capture packets directly from a network interface, or analyze data from a previously saved file. While capturing data, Ethereal can give you real-time statistics about which protocols are actively in use (Figure 3-35). Start capturing by selecting Capture → Start..., select the interface you want to capture from, and click OK. Note that you need proper permissions (typically root privileges) to actually capture data.

Figure 3-35. Ethereal gives you statistics about the protocols it sees as it captures packets.

If you would like to see these statistics again (with even more detail) after you have finished capturing packets, go to Tools → Protocol Heirarchy Statistics. You can use this on previously captured dump files as well. If you already have some captured data (say, saved with tcpdump from a remote machine), you can simply click File → Open... and select the file you’d like to analyze.

Ethereal displays the data it has collected in three ways. The top part of the window shows a summary of the data, with one packet per line. This lists the sequence, time, IP data, protocol, ...