I stumbled upon a fantastic RFC - Evolution of IP Model (RFC 6250) - that should be made mandatory reading for everyone remotely involved with networking. It describes numerous "truths" (politely called misconceptions) that everyone from programmers to network designers still rely upon. Some of my favorites: reachability is symmetric and transitive, loss is rare, addresses are stable, each host has a single interface and a single IP address ... Enjoy!
Ivan Pepelnjak, CCIE#1354, is the chief technology advisor for NIL Data Communications. He has been designing and implementing large-scale data communications networks as well as teaching and writing books about advanced technologies since 1990. See his full profile, contact him or follow @ioshints on Twitter.