On Wed, 22 Nov 2000, Richard Draves wrote:
> Hmm. I don't see the connection. The RA preferences are for router
> selection, not source address selection. Are you suggesting that the two
> should be connected somehow?
Would you always pick a longest match for source address over the RA
that had the best preference?
For example in the selection draft you say
"For example, suppose a node has interfaces on two different links,
with both links having a working default router. Both of the
interfaces have preferred global addresses. When sending to a global
destination address, if there's no routing reason to prefer one
interface over the other, then an implementation MAY preferentially
choose the outgoing interface that will allow it to use the source
address that shares a longer common prefix with the destination."
The RAs now convey "routing reasons", which affect the selection (in that
without them, another choice might be made).
Of course, this may be exactly want you want, but I suspect the common
"multihomed" scenario at present is sites with a 2001: link and a 3ffe:
link, one of which is probably much better than the other, even though
both may route happily anywhere.
> > I'm also interested in just how the routers will be configured to make
> > the advertisements, as it would seem this would impact the router
> > renumbering process?
>
> My first thought is that this should not impact router renumbering. Router
> renumbering is about making configuration changes uniformly across a set of
> routers, while the advertisement of default router preferences &
> more-specific routes is very topology dependent. I think it's something that
> an administrator would need to selectively configure on relatively few
> routers, not configure uniformly across a site.
The question is how deeply the "topologically dependent" changes are made
by the administrator through the network. Having manually configured
preferences in the config file only adds to the list of things that (might)
need changing if the network is renumbered, or a network you're giving a
preference to is renumbered? I appreciate there are other issues such as
IOS access lists and of course IPs embedded in host configs. How realistic
a goal is (relatively) transparent renumbering?
Tim
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