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Re: classful routes redux

  • From: Marshall Eubanks
  • Date: Sat Nov 05 13:15:18 2005


On Nov 5, 2005, at 12:01 PM, Geoff Huston wrote:

At 03:09 AM 5/11/2005, Christopher L. Morrow wrote:

On Fri, 4 Nov 2005, Russ White wrote:
> - -- BGP is currently moving to a 2^32 space for AS numbers. That's odd,
> if there's only 18,044 origins in the current table, and it won't ever
> grow to much more--how'd we lose 40,000 or so AS numbers, that we now
> need more than 64,000?

I think someone at CAIDA or even Renesys could put out some good numbers
for 'origin' AS counts and even 'AS in aspath' It's slightly higher than
18k, but not 40k higher :) At last look (during arin/nanog meeting) it was
about 20k unique origins (from 701 perspective as seen through

As of a few minutes ago there are 21.042 unique ASs seen in Route- Views.

From the multicast status page,

I get a total number of Active Unicast AS seen by BGP = 20660 (a little smaller than Route-Views), and a total
of 22038 having _ever_ been seen by BGP announcements here (since April, 2001).

There are clearly more AS's in use out there in non-public networks, as seen, e.g., by the steady
dribble of low number DOD ASN's that leak out from time to time, but it does
not seem that this pool is very large.

Marshall Eubanks

13,997 are origin onlu (i.e. they are not seen in the middle of an AS path), 66 are transit only and 6.979 are mixes origin + transit.

8,554 ASs announce a single prefix, while the average announcements per origin AS is 9.1 (the reason is a heavy tail distribution where a small number of ASs originate a very large number of prefixes)

The average address span for an origin AS is 70,426 /32s (or slightly larger than a /16) Again this is a heavy tail distribution.

(more time series data on the routing table than you'd ever want is at and

The overall trend is the association of fewer addresses per originating AS, pointing to a trend to impose ever finer levels of policy delineation within the inter-domain routing mesh at places closer to the edge of the network - i.e. multi-homing and traffic engineering within an increasingly dense interconnection mesh appear to be one of the major motivations here for the continued consumption of AS numbers. The CAIDA skitter graphs are perhaps the most dramatic way I've encountered so far that clearly shows this trend.



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