Comment by gcb0

But a firewall I can open. heck most consumer routers came preinstalled with holes on the firewall/NAT for FTP,IRC,MSN and a bunch of long dead protocols that required the server to connect to the client...

with ipv4+nat often I can't allow a connection because i don't have the IP visible. i'd have to have the server to add my internal IP (which will surely conflict) to their routing table passing trhu my external IP on the router.

This is the problem ipv6 solves.