Tcpdump

tcpdump is a command used to dump network traffic for TCP/IP networks.

The information can be used by a wide variety of network analysis programs, either via piping or by saving the stream to a file for later analysis.

Using a filter expression to tcpdump you can select to dump only a certain protocol or a direction of packets. For example, you can filter on port: tcpdump -i eth0 port 80 In this case, you only show network packages on port 80 of the network card eth0.