AS number consolidation

Mon Jun 2 15:08:49 UTC 2003

I just spoke with a couple of the people involved in the SBC transition
and they are thinking about putting a presentation for a NANOG after
they transition the former Ameritech ASes. 

This is a truly massive undertaking merging around 100 ASes from coast
to coast and re-aggregating all of the routing and, from my viewpoint,
have done an amazing job. I hope they do the presentation.

R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634

> Date: Fri, 30 May 2003 09:03:54 -0500 (CDT)
> From: Daniel Golding <dgold at FDFNet.Net>
> Sender: owner-nanog at merit.edu
> 
> 
> SBC just did one of the largest AS merges ever accomplished. Maybe one of
> their engineers will give a brief report? One item to always look out for,
> if you have BGP-speaking customers is the particular implementation of
> "local-as" on your favorite brand of router. There are some variations...
> 
> - Some include the "imposter AS" in the AS path
> - Some have a keyword for stripping out the "imposter AS"
> 
> The vendor documentation on this feature has been historically weak,
> necessitating some lab work.
> 
> This can be an issue, as you could be accidentally prepending route
> announcements learned from your downstreams by having both the new and old
> AS in the path.
> 
> Thanks,
> Daniel Golding
> 
> On Fri, 30 May 2003, David Luyer wrote:
> 
> >
> >
> > > Does anyone know of case studies of companies collapsing
> > > multiple ASes
> > > into one on their network? I have the Allegiance Telecom
> > > presentation from
> > > NANOG 27 but I would like to hear how other people have done
> > > it as well.
> >
> > We have to date collapsed 6 AS numbers into 1.
> >
> > Approach was relatively simple - but it's been at
> > least a couple of years since the last merge so I'm
> > a little light on exact memory/detail:
> >
> >   1.  Duplicate RADB (or other) entries across to new
> >       AS.
> >
> >   2.  Merge interior routing protocols across the ASen
> >       which are about to be merged.
> >
> >   3.  Gradually grow the largest AS adding a router at
> >       a time (notify the BGP peers on the router, set a
> >       time, make the change).
> >
> > To me this is one of the things where you can go over the
> > top in planning (I know an ISP who have been planning an
> > AS merge for years) or you can 'just do it'.
> >
> > The second hardest thing, if you bother to do it, is
> > "cleaning" the old AS (in terms of RADB, other registries,
> > route filters in peers, etc) before returning it to the
> > registry.
> >
> > The hardest thing is convincing the registry to take them
> > back... (you'd think that'd be easy, but it took by far
> > the longest of the whole job).
> >
> > David.
> >
> >
> 