AS number inconsistencies

Mon Jul 8 14:18:23 UTC 2002

On Mon, 8 Jul 2002, Marwan Fayed wrote:

> I am a CS PhD student trying to track ASes (for reasons I'm happy to
> discuss offline). There is a grave inconsistency I have come across and
> can't explain. Simply, there seems to be many AS numbers in the
> non-private range that come into use at some point in time and advertise a
> range of IPs, but these AS numbers are not allocated until much later.
>
> More specifically, archived BGP tables show many AS numbers which ARIN
> shows not to have allocated (in their allocation history tables) until
> many months, sometimes a year/two, later. The number of such ASes has
> shrunk over time (from about 100 in 1999/2000 to 20-30 in 2002) but still
> exists. I don't want to "name ASes" <grin>.
>
> Does any one have any explanations? Are network operators "notified" of
> their new AS number well in advance of the actual receipt of that number
> on paper, for example? Any help is appreciated (and hopefully this
> occurence is of interest to nanog).

The most plausible explanations I can think of for people not using their
ASNs in their production networks for a long time after receiving them
from their RIR are:

1) There are technical challenges to be overcome before the AS can start
to originate routes.  For example, the AS migrations, or some other large
network cutover or architecture change.

2) After the ASN is allocated, business/technical drivers shift as they
often do in this industry, and the project that required the new ASN is
now pushed back/scaled down/eliminated entorely.

I've seen examples of both "in the wild".

jms