On Fri, 14 Oct 2005, Paul Vixie wrote:
david.conrad@nominum.com (David Conrad) writes:
(shouldn't that be drc@iana.org now?)
If my impression is correct, then my feeling is that something else is required. I am somewhat skeptical that shim6 will be implemented in any near term timeframe and it will take a very long time for existing v6 stacks to be upgraded to support shim6. What I suspect will be required is real _site_ multihoming. Something that will take existing v6 customer sites and allow them to be multi-homed without modification to each and every v6 stack within the site.
if all you've got is a hammer, every problem looks like a nail. so, the above problem statement looked like a dns issue to me, and to some other folks, and thus was born A6. had ietf killed AAAA back when there were effectively zero ipv6 hosts on the 'net, and paid the apparently-high A6 complexity penalty, we'd be talking about something else by now. as it is, the shim6 complexity penalty is even higher, and i don't think we'll ever get to stop talking about this problem.
Paul, I was big fan of A6 design and very sorry to see it discarded by IETF. But I do not believe it would have solved quite the same problem as what shim6 is trying to do (I'm not saying that it could not solve it with additional ipv6 extensions...). A6 was particularly good for solving problems of renumbering and allowing site to have same local ip address configuration for multiple ISP connections which can allow easy load balancing through DNS. But once connection is established it would be normal end-node<->end-node IPv6 connection with full 128bit ip6 addresses used for each side. That means that if connection goes down it would not be able to automatically do a fail-over (nor would dns load-balancing similar to current one with listing multiple A addresses do failover to use only active and working ipv6 connection). What I do think is that A6 and shim6-like design would have been a good compliment to each other. In this case the end-site network address (i.e. part above /48) would have been the same and is the one configured on switches and servers and listed as host address. The domain reference (i.e. common to multiple hosts) would point to the ISP networks A6 network addresses (i.e. part below /48) and is the only thing one changes when moving from one ISP to another (no renumbering!) or when connecting to 2nd ISP. If multi6 is used then additional special reference is made to multi6 network address (special reserved network block non-routable block) and multi6 aware clients would use that as common ip6 address reference for upper layers (i.e. in TCP and UDP) and let very simple multi6 layer keep track of local host's resolution of this address to real A6 networks. -- William Leibzon Elan Networks william@elan.net