AT&T NYC

Tue Sep 3 12:35:32 UTC 2002

On Tue, 3 Sep 2002 alex at yuriev.com wrote:

> > > > > 
> > > > > > > Has anybody mentioned the benefits of ISIS as an IGP to them.
> > > > > > 
> > > > > > Link-state protocols are evil, and when they break, they *really* break.
> > > > > > I still do not see a compeling argument for not using BGP as your IGP.
> > > > 
> > > > Convergence time?
> > > 
> > > What is better - relatively long convergence time on affected routes or a
> > > problem on unaffected route?  
> > > 
> > > Ask your customers. They do not care if someone else is having a problem.
> > > They care that they dont. 
> > 
> > Do you run a decent sized network?
> 
> No, I have never touched a router in my life. 

Possibly..

> > Convergence time in the order of that taken by BGP is not acceptable,
> > things go crazy when traffic pours in and theres no routes to carry it.
> 
> This is a great blanked statement. What is convergence time?

The time from when traffic starts hitting down interfaces or null to when it
starts going again. Preferably without the rest of the network needing to know
about it and suffer meltdown.

> > Other example, what about static dialup users, they dial up and wait a few
> > minutes whilst their route is installed throughout BGP??
> 
> That is why their route is *nailed* via BGP to the router that *always*
> provide connectivity to them. If they have to move, BGP injectors are your
> friends. Takes seconds.

See previous comment about network size - theres no such thing as always in
dialup with multiple geographic PoPs.

> > > > > With link-state, one interface flap can mean doing SPF on every route.
> > > > > If "every route" is only a couple hundred, rather than 100K, you fare
> > > > 
> > > > As you say disable synchronization and try and control the physical reach of
> > > > your igp by some mechanism.. areas, summaries, ASes etc
> > > 
> > > Which is exactly what you are doing when you inject nailed routes into bgp.
> > 
> > No its not? I'm suggesting some level of order can help control the number of
> > routers required to reconverge a network, I dont see the comparison with
> > inserting routes in BGP which is how the routes get in not how they converge.
> 
> If you dont have a network wide meltdown due to IGP failure you wont need to
> wait for entire network to come up. It is timing of discrete events.  Isn't
> math grand.

Reconvergence after a single link failing is hardly failure/meltdown?

Steve

- Bored of arguing - private responses only

> 
> Alex
> 
> 