North American Network Operators Group

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RE: AS number consolidation

  • From: David Luyer
  • Date: Fri May 30 08:19:38 2003

> 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

  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

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).