[c-nsp] BGP Fast-external-fallover

[Daniel Roesen]

On Sun, Mar 13, 2005 at 07:43:33AM -0800, David Barak wrote:
> > Actually, your provider does a service to you. When you fixed your
> > flapping for good, you can call your provider and have him reset
> > the damping holddown. 
> 
> So the burden goes from the provider to the customer? 

I can't follow this conclusion at all. Your session flaps, your ISP
dampens the flapping. When flapping is fixed, the damping is cleared
and you have connectivity again via this upstream immediately. The
other scenario would mean that you have 30-60 minutes of bad to no
connectivity after the flapping is being fixed via this upstream.

Another advantage: while one of your uplink sessions flap, you have
still stable connectivity, and routing stays stable (after the flapping
session is being dampened), and you avoid convergence blackholing etc.

> > If he would pass this flapping on, all/most/many
> > peers/upstreams of him would have your prefix dampened, and almost
> > nothing he can do about it. You stay down until all their reuse
> > timers expire.
> 
> But if you postulate an enterprise with N locations,
> the other N-1 locations will find the location with
> the flapping circuit completely unreachable, rather
> than only partially unreachable.

If you speak BGP, you are multihomed. You don't lose connectivity
completely.

> > Propagating the instability hurts more than damping
> > it early at the source.
> 
> Dampening, like bogon filtering, is something which is
> a good idea in theory, but in practice, can do far
> more harm than good, unless it's very, very carefully
> managed.  

Of course. People doing BGP who don't know what they do usually do more
harm than good. And obviously there are still misconceptions about
dampening out there.

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Regards,
Daniel

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