Napster, WinMX, Gnutella, and KaZaA are peer-to-peer file sharing system that is very much like IRC. Until recently, most Napster users used the Napster network; there are other networks that can be accessed through Napigator. The OpenNap server stores filenames and (for audio files) data rate and duration information. Unlike and, a Napster server stores no file data; instead, the file is sent directly from peer to peer. At locations with extremely limited bandwidth to the Internet (due to overselling; for example, Rose-Hulman Institute of Technology has four T1 lines, the effective equivalent of 120 so-called "56K" modems, for 1500 students), this file transfer severely eats into the web surfing experience of other users.

Network admins could solve this problem by restricting the ports that P2P uses to 15% of total throughput, or they could run their own OpenNap server within the LAN, accessible only from inside the netblock, and block other popular servers (transparent proxying anyone?). This way, file transfers will go from one peer on the 100 Mbps LAN to another peer on the same LAN; a 4-megabyte file that goes over the LAN is four megabytes of data (plus half a meg of TCP headers) that does not need to cross the T1 lines.