in reply to perl IP packet sniffer
There is also the CoralReef suite of tools at
http://www.caida.org/tools/measurement/coralreef/
From the webpage: CoralReef is a comprehensive software suite developed by CAIDA to collect and analyze data from passive Internet traffic monitors, in real time or from trace files.
Perl API, docs at: http://www.caida.org/tools/measurement/coralreef/doc/doc/libcoral-perl.html
In Section
Seekers of Perl Wisdom