North American Network Operators Group
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Re: BGP and aggregation

  • From: Stephen Griffin
  • Date: Sun May 12 18:35:39 2002 
In the referenced message, Andy Walden said:
> On Sun, 12 May 2002, Stephen Griffin wrote:
> 
> >
> > In the referenced message, Andy Walden said:
> > >
> > >
> > > Conditional Router Advertisement:
> > >
> > > http://www.american.com/warp/public/459/cond_adv.pdf
> > >
> >
> > As it sounds like he's using a single AS, the above may not be
> > a fix, since a partitioned AS is still a failure condition.
> 
> Why?
> 
> If you announce one prefix via one circuit and announce a different
> prefix via a different with the same source AS, I don't see a problem
> since traffic will continue to reach its intended destination.
> 
> andy

BGP will discard any prefix with its own AS in the path, for loop
prevention. Hence, one half of the AS would still be unable to
reach the other half. This is why a partitioned AS is a failure
condition. A tunnel is a means to keep the AS nonpartitioned.

There are other ways to treat the symptoms, but they aren't
particularly good, imho.