Chapter 8. Tcpdump
Overview of Tcpdump
Most network administration tools are not based directly on the data being transmitted on a network, but rather on information related to that data. MRTG, for example, uses network bandwidth values. Other tools make use of system logs on network equipment or they test for system availability. It is sometimes necessary, however, to examine the packets themselves. Doing so will allow you to diagnose some particularly tricky network problems and can also serve as a hands-on approach to learning more about network protocols.
The most widely used open source tool for directly analyzing packets is a program called tcpdump, originally written by Van Jacobson. The standard tcpdump, through version 3.4, is maintained ...