Great impromptu intro video to the Bro Security Network Analysis Framework at Shmoocon by one of my favorite security authors/ speakers Richard Bejtlich.
Bro is an amazing tool that gives you a great summary of what is going on in your network. It creates text log files of connections, protocols, communications, and whatever else it sees on the wire. Check it out, this is good stuff. And I know I have been on a Security Onion kick again, but guess what? It comes installed by default in the open-source Security Onion IDS .
Just surf to your nsm/bro/ directory and check out all the log information created for you.