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tcpdump is the name of a popular computer network debugging and security tool which allows the user to intercept and display TCP/IP packets being transmitted or received over a network to which the computer is attached. On UNIX and most other operating systems, a user must have the equivalent of root or system administrator privileges to use tcpdump.

The user may optionally apply any number of filters to render the output more usable on networks with a high volume of traffic.

Common Uses of tcpdump

tcpdump is a command line, text mode only program. Ethereal is a similar program with a GUI frontend, and many additional formatting, sorting, and display facilities.