Re: failure detection

[Erik Nordmark <erik.nordmark@sun.com>]

Paul Jakma wrote:

> One thing though: from the POV of the router which wants to change RA's 
> due to link-failure, it has no idea of how temporary the failure is. So 
> maybe call it 'failed' instead? But that implies continuing to send RAs 
> for the prefix.

"failed" is about right. The semantics is basically a recommendation to 
hosts to not use that prefix, and if possible switch to using other 
prefixes.

But one of the tricky aspects is that the prefix might work perfectly 
for traffic internal to the site, and it is only external traffic that 
is effected. I don't know how easy it is to convey that notion to the 
hosts, since the hosts don't know how large prefix is assigned to the 
site (assuming it is and always will be a /48 is probably a bad idea).

> Maybe because no one is interested in multi-prefix IPv6 sites until 
> solutions like shim6 are available?

But even if that is the case, we still need to handle the case when the 
peer host doesn't support shim6.

> > So it's not clear to me whether such a mechanism would be limited to 
> > the single link site where the RAs come directly from the border router.
>
>
> Hmm, I guess yes. The multi-router case and protocol for distributing 
> external link-availibility seems a general one.
>
> I guess an implementation could offer a facility to 'pin' RAs to a 
> specific prefix announced in IGP. IGP withdraws route, the routers RA 
> code either stops sending RAs for that prefix or uses the 'failed' bit?

You mean pinning it to a route for some external prefix?
Presumably we want things to work when a site has multiple exits and 
each ISP just advertises a default route into the site.

   Erik