AS migration

Josh Fleishman flyman2 at
Tue Jan 22 21:38:56 UTC 2002

Beer?  Sushi?  Beer?  I'm in.

As Miguel noted, we at Earthlink/Mindspring/OneMain continue our ongoing
AS integrations(we have over 30).  A few additional gotcha's and
benefits that come to mind you might want to consider include better IP
space utilization, elimination of backdoor routes, radb updates, use of
NSSA/TSA, peering benefits, and the use of 'local-as' options.

IP space utilization can be benefited by consolidating IP space into
larger and more useful aggregates.  Which also results in better
announcements, and a happier NANOG community :).

Backdoor routes based on the integrated AS's, if currently used, become
obsolete.  A minor detail.

RADB updates should be made so that your IP space is correctly
registered to the kept AS#.  Particularly important if any of your
transits/peers base their filters on such a database.

Not-so-stubby and totally stubby areas, if they fit your design, are a
good way to prevent over-load of your smaller routers with an increased
LSDB size, and especially if you have a lot of redistribution going on
in your network.

If you are interested in peering, presenting your network as a single AS
where you can advertise routes consistently in multiple locations is
another great benefit and helps meet some of the more stringent peering
requirements.  Without going too much into the value of peering, if done
correctly your overall transit costs can be significantly reduced as
well as better latency for your users.  (This is a good way to impress
the boss.)

By specifying the local as, you can integrate IGPs and build your
confederation completely transparent to the outside world.  Junipers and
Cisco's, among others, both support this option.  Note, the last I
checked you can't specify different local AS#s for peers within a Cisco
peer group.

This is only a start..  It's not overly difficult, and depending on the
size of your network (and staff), probably worth it.  

Justin, I'd be happy to share our experiences with you sometime at


Josh Fleishman
Sr. Network Engineer/Peering Coordinator

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