I first saw this while training for CISSP. It may not be 100% accurate if you're being picky, but it does give a good visual representation of the inner workings of a network. Took me a while to find, but finally got it at Google Video Search:

http://video.google.com/videoplay?docid=-5019530929128132102&q=network+animation

Interesting animation of the life of a packet as it travels through the network. Stars of the show include a TCP Packet, ICMP Echo Packet, UDP Packet, Router, Switch, Ping of Death and a supporting cast of millions.


Hope you enjoy,
Don