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Re: Multi-6 [WAS: OT - Vint Cerf joins Google]

  • From: Bruce Campbell
  • Date: Sun Sep 11 15:24:23 2005

On Sun, 11 Sep 2005, Richard A Steenbergen wrote:

On Sun, Sep 11, 2005 at 06:32:58AM +0200, Mikael Abrahamsson wrote:
Giving each entity who wants to multihome an AS of their own and own
address block, doesn't scale. Think this in the way of each home in the
world being multihomed, it just doesn't scale.
To quote some stats from the latest weekly routing table report to hit
nanog:

BGP routing table entries examined:                              169983
Total ASes present in the Internet Routing Table:                 20445
Origin-only ASes present in the Internet Routing Table:           17787
Origin ASes announcing only one prefix:                            8431

This says that although there are 170k prefixes on the Internet, there are
only 20k entities who actually need to announce IP space. There is only
one explanation for such a large difference (8.5x) between these two
numbers, namely that people who are announcing IP space need multiple
blocks in order to accomodate their needs.
Actually, you've missed two crucial lines from the report:

Prefixes after maximum aggregation: 97203
Unique aggregates announced to Internet: 82000

That implies that 73k (170k - 97k) worth of announcements are related to traffic engineering tricks, multihoming, poor education or simply 'because'. ( A decade on and there are still books/routers/courses/people which don't grok CIDR )

A further 15k (97k - 82k) worth of announcements seem to be duplicates;
multiple paths being naturally seen or intentionally announced.

Of the 82k worth of possibly unique prefixes, 8k worth of those are from ASes announcing solely one route. The remaining 74k prefixes are announced by 9k ASes; 8 each.

the majority of these prefixes are due to IP
rationing, which forces growth into multiple blocks.
An interesting question to ask, before you point at IP rationing being the main cause, is how many entities that have received IP allocations also have ASes? In other words, these ASes having 8+ prefixes each may in some cases be a single ISP announcing the routes of 5 seperate customer entities.

A further question to ask would be, considering that issuing IPs is the RIR's business, why haven't the RIRs noticed a tendency for certain entities to keep coming back for more IP space, and thus why haven't the RIRs been putting aside aggregatable IP space for these entities or been notifying their membership on the possible need for a change in addressing policies to avoid such problems ?

Certainly, I'll agree that IP rationing (via RIR policies) is responsible for a certain, hopefully small, percentage of non-aggregatable prefixes. But I don't think that IP rationing is responsible for the majority of such prefixes.

--
Bruce Campbell

Then again, I may be biased ;)




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