IPP2P

The goal of the IPP2P project is to identify peer-to-peer (P2P) data in IP traffic. For this purpose we extended the iptables/netfilter architecture by a new matching module. Thereby IPP2P integrates itself easily into existing Linux firewalls and it's functionality can be used by adding appropriate filter rules.
IPP2P uses suitable search patterns to identify P2P traffic thus allowing the reliable identifcation of traffic belonging to many P2P networks. Once identified one may handle P2P traffic in different ways - dropping such traffic, putting into low priority classes or shaping to a given bandwidth limit is possible. Reducing costs, freeing network ressources and therefore improving network performance is often the result of using IPP2P.

http://www.ipp2p.org