[klodolph]

Packets aren’t created equal. Don’t think of a network as just a medium which lets you send packets from point A to point B. It’s a reasonable simplification but it’s not accurate!

Routers read the contents of TCP packets to figure out the state of the TCP connection, and then make decisions based on the state of that connection. With UDP that doesn’t work. This makes a HUGE difference for NAT. With UDP, there’s no connection and no state, so at best a router might guess correctly using some loose heuristics, but at worst the router will just drop your UDP packets on the floor.