That's once again a matter of defaults -- routers should _by default_ discard all packets from interfaces which they won't use for forwarding those packets back.
This is a sweeping statement. I'm not sure we should buy into it without thinking about it pretty hard. However, I am no routing theorist, so maybe this has already been thoroughly explored by the high-level networking gurus. I see three obvious advantages: 1. Prevention of IP spoofing. 2. Prevention of asymmetric routing. 3. Better TCP windowing and better performance when all packets follow the same path. However, are the benefits worth the overhead? What are the effects on network redundancy? What other issues am I overlooking? -- Jerry Anderson jerry@gi.net Principal Engineer (402) 436-3030 Implementation & Consulting http://www.gi.net/jerry Global Internet Network Services (formerly known as MIDnet)