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