Not quite true. Some machines can't be reached. Many others have UPnP capable routers and can reconfigure NAT for port forwarding on the fly. Additionally mor

Not quite true. Some machines can't be reached. Many others have UPnP capable routers and can reconfigure NAT for port forwarding on the fly. Additionally more and more users have IPv6 at home. It's now high enough to be worth trying along with other techniques like STUN.