Why Do We Need Source IP Addresses in IP Headers?
After discussing names, addresses and routes, and the various addresses we might need in a networking stack, we’re ready to tackle an interesting comment made by a Twitter user as a reply to my Why Is Source Address Validation Still a Problem? blog post:
Maybe the question we should be asking is why there is a source address in the packet header at all.
Most consumers of network services expect a two-way communication – you send some stuff to another node providing an interesting service, and you usually expect to get some stuff back. So far so good. Now for the fun part: how does the server know where to send the stuff back to? There are two possible answers1: