> There is some relevant text in RFC 3484: > > Implementations may also use the choice of router to influence the > choice of source address. For example, suppose a host is on a link > with two routers. One router is advertising a global prefix A and > the other router is advertising global prefix B. Then when sending > via the first router, the host may prefer source addresses with > prefix A and when sending via the second router, prefer source > addresses with prefix B. > > This provides guidance in the right direction, but I'm not sure if it is > sufficient, or ever implemented.
As others have said the above language is really weak. But even if the language was a MUST and it was universally implemented I don't think it would help; other issues would have to be resolved. For instance, what should the host do when it suspects that the 1st hop router is down? (e.g. due to NUD failing) In the model that all routers on the link are assumed equal, the host, as is specified in RFC 2461, can switch to using a different 1st hop router. But in what I would call the source based routing model (where the source address determines which 1st hop router is used), switching to a different 1st hop router might be a bad idea (ingress filtering above that router might discard all such packets); continuing to send packets to the 1st hop router that advertised the prefix might actually be better - in case the router receives the packets they will make it to the destination. Thus I thing there is a rather large architectural question lurking in this issue. *If* we want to pursue this path at a minimum the host needs to know whether using the original 1st hop router is better or not. One way to do this is to require that routers on the same link must advertise the same set of prefixes (and make the router advertisement consistency in RFC 2461 check this?). If we did that then the hosts could assume that when different routers advertise different sets, the routers are not managed by the same entity and the host should use a 1st hop router that is consistent with the source address. But the host could switch 1st hop routers among the set of routers that advertise the same set of prefixes. I don't know whether we could make the operational requirement that the routers on the same link (that don't want source-based routing) must advertise the same set of prefixes stick. Depends on what the current operational practices I guess. Erik -------------------------------------------------------------------- IETF IPv6 working group mailing list [EMAIL PROTECTED] Administrative Requests: https://www1.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
