RE: Preserving established communications (was RE: about draft-nordmark-multi6-noid-00)

["marcelo bagnulo" <mbagnulo@ing.uc3m.es>]

> > The problem is that to detect that there is no route to a certain, all
> > the
> > alternative routes with increasing AS path are tried, which is
> > inherently
> > slow.
>
> Only if there are no alternatives. If there are, the path for those is
> probably not that long so they show up pretty quickly. Only when the
> last/only path goes down you'll see the following problem:

Ok, but this is the case that we care, right?
From ISPA prespective, there is no longer a route to the destiantion, so the
multi-homed site detects that and tries the alternative ISP (ISPB).
So the case that we care is the reconvergence of BGP within the portin of
the network where a route to the destiantion address no longer exist

>
> > This would be similar to the count to infinity problem, but with
> > different AS path.
>
> But we usually don't care since when our last/only path goes down we're
> unreachable anyway.

I don't see it that way, i mean, the destiantion *is* unreachable through
one of the providers. The route is withdrawn from that part of the network.
Then once that the route has been withdrwan from that part of the network,
the multihomed site detect the problem and tries with the alternative ISP.

Anyway, i guess that the reconvergence time is only part of the problem.
Another part of the problem is the time required to detect the outage. Only
this factor would render the solution inacceptable for many applications.
Regards, marcelo