Argus is a generic IP network transaction auditing tool that has been used 
by thousands of sites to perform a number of powerful network management 
tasks that are currently not possible using commercial network management 
tools.

Argus runs as an application level daemon, promiscuously reading network
datagrams from a specified interface, and generates network traffic audit
records for the network activity that it encounters.  It is the way that
Argus categorizes and reports on network activity that makes this tool
unique and powerful.

WWW: http://www.qosient.com/argus/