John and Lorenzo beat me to it :). Example: Samantha has native IPv6 and Teredo. Albert has Teredo only.
Albert, in destination address selection, will chose Samantha's Teredo address. Samantha, in source address selection, will use her Teredo address. This will avoid relay traversal. Xbox P2P policy is a bit more sophisticated than RFC 6724, but I note that the avoidance of Teredo relays is also part of Windows behavior. Windows address selection is a fairly clean implementation of RFC 6724. In RFC 6724 terms, Teredo -> Teredo is a label match (Rule 5), Teredo -> Native IPv6 is not. The biggest difference between us and the standard is the brokenness check. This does complicate the dream. In order for a set of peers to use native IPv6 - BOTH peers have to have native available. In the pathological case, if half of the world has IPv6 and connects only to the other half that only has Teredo, and no one actually uses native IPv6. Realistically, matchmaking is going to prefer users "close to you" (and a bunch of other things, like their gamer behavior and stuff). Naively I expect IPv6 traffic to start as local pockets, Albert playing against his neighbor, both with the same ISP. As IPv6 penetration grows hopefully we'll see significant P2P traffic across the Internet use native IPv6 transport. From: ipv6-ops-bounces+christopher.palmer=microsoft....@lists.cluenet.de [mailto:ipv6-ops-bounces+christopher.palmer=microsoft....@lists.cluenet.de] On Behalf Of Lorenzo Colitti Sent: Wednesday, October 9, 2013 8:26 PM To: Geoff Huston Cc: IPv6 Ops list; Christopher Palmer Subject: Re: Microsoft: Give Xbox One users IPv6 connectivity On Thu, Oct 10, 2013 at 12:19 PM, Geoff Huston <g...@apnic.net<mailto:g...@apnic.net>> wrote: But I've thought about your response, and if I'm allowed to dream (!), and in that dream where the efforts of COmcast, Google etc with IPv6 bear fruit, and I'm allowed to contemplate a world of, say, 33% IPv6 and 66% V4, then wouldn't we then see the remaining Teredo folk having 33% of their peer sessions head into Teredo relays to get to those 33% who are using unicast IPv6? And wouldn't that require these Teredo relays that we all know have been such a performance headache? Can't you fix that by telling the app "if all you have is Teredo, prefer Teredo even if the peer has native IPv6 as well"? Of course this breaks down when IPv4 goes away, once IPv4 starts going away then there's really way to do peer-to-peer without relays, right? (Also, IPv4 going away is relatively far away at this point.)
