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

Sun Sep 11 19:23:14 UTC 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 ;)