[ppml] NANOG IPv4 Exhaustion BoF

Geoff Huston gih at apnic.net
Fri Mar 7 03:17:53 EST 2008

John Curran wrote:
> At 5:39 PM +1100 3/7/08, Geoff Huston wrote:
>> Yes, the situation the this industry has driven itself into is messy, but
>> I'm pretty sure that global collapse is not exactly on the agenda.
>> ...
>> What I would claim is that this transition is just another risk factor
>> in an industry that has its fair share already and doubtless will
>> continue to have its fair share in the future.
> I'd agree with you if there were anything resembling a useful
> feedback mechanism on the global routing table. 

The sad fact is that the global routing table has been under 
concentrated assault by the legions of /24s for many years now.

Since 2001 50% of the routing table is more specifics - and now there 
are 135,208 of them. My supposition is that TE is the major factor - 
when you look at highly deaggregated prefixes you tend to see a 
collection of upstreams and load spreading across the upstreams.

So in many ways the routing system is already under this "fragmentation" 
pressure and will remain so whether its IPv4 or IPv6 (and I suspect at a 
more meta level, efforts to reintroduce aggregation into the routing 
system, if adopted would not have much impact in changing the current 
numbers by very much simply because of these TE pressures). What we 
route across is the cross product of the number of distinct entites, the 
level of interconnection between entities and the desired/imposed level 
of diversity of path. And as the network expands the value of this cross 
product will rise, transfers, minimum size limits, or any other factor 
nowithstanding, and the routing table will continue to inflate at a rate 
that is higher than the number of distinct routing entities.

So what I'm saying is that the routing system is an expression of a more 
basic metric of the network's interconnection, and that this value will 
be expressed in the routing system irregardless of the particular 
routing technology and irrespective of the varioous address policies 
that we may state.

As I understand your argument here John its that fragmented address 
supply won't make it any better, but it could make it worse, and that 
could trigger responses such as selective filtering, threatening global 
connectivity. Yes, thats a valid concern. Without much data to quantify 
the risk its hard to assess how critical this factor will be.


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