This was posted in retrofocus (http://www.securityfocus.com/infocus/1674), it's about IP spoofing, it was originally posted on March 11, 2003.

Now there is a link in it that I found a very interesting read as I didn't know about security issues with RIP, EGP,... (Maybe those RIP issues have been solved in RIP2 as the document is from 1989, don't know about that)

Read it here: http://www.ja.net/CERT/Bellovin/TCP-..._Problems.html