A utility found on many UNIX(-ish) systems to monitor the activity on a network interface.
It can `dump' raw network data, as well as nicely format the lines (i.e. a hostname, portnumber, and connection type are printed).
Altough the name suggests it only dumps TCP connections, it catches UDP and other types of connections too.
Written by Van Jacobson, Craig Leres and Steven McCanne from the Lawrence Berkeley National Laboratory, University of California in 1988. Distributed under the terms of the BSD License. | 
