North American Network Operators Group

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Re: multi-homing fixes

  • From: Iljitsch van Beijnum
  • Date: Wed Aug 29 18:21:31 2001

On Wed, 29 Aug 2001, Clayton Fiske wrote:

> > > the /24s of small multihomers is half the routing table (see geoff's data)

> > This can't possibly be correct. The last figure I read was that there are
> > about 70k /24s. There are about 21k AS numbers out there. This means that
> > by far most of the announcements, including /24s, are the result of lack
> > of CIDR. Either because ISPs have a relatively large number of PA blocks
> > (address conservation) or because of lack of aggregation.

> Small multihomer /24s aren't necessarily their own. I've dealt with plenty
> of customers multihoming with a /24 from their other provider without
> running BGP. No extra AS number, but the /24 still shows up in the global
> table. Also seen customers with their own /24, but having us originate it
> rather than doing BGP with them.

I've never dealt with a customer with such a setup, but with at least a
dozen BGP multihomers. I'm sure that people are multihoming this way, but
I'm not so sure these BGP-less multihomers make up half the routing table.
I've tried to gather some statistics. They aren't very good, but what I
got was 1209 "inconsitent paths" below 212.x.x.x.

Apart from the people who don't aggregate the high number or /24s in the
global routing table is probably also to a large extent due to people not
wanting to renumber and taking addresses with them to another ISP.