a radical proposal (Re: protocols that don't meet the need...)

Iljitsch van Beijnum iljitsch at muada.com
Thu Feb 23 18:58:52 UTC 2006

On 16-feb-2006, at 0:15, Fred Baker wrote:

> On Feb 15, 2006, at 9:13 AM, Edward B. DREGER wrote:
>> Of course not.  Let SBC and Cox obtain a _joint_ ASN and _joint_  
>> address
>> space.  Each provider announces the aggregate co-op space via the  
>> joint
>> ASN as a downstream.

> Interesting. This is what has been called metropolitan addressing.  
> I'm certainly not the one who first proposed it, although I have  
> thought about it for a while, dating at least as far back as 2001.

> The crux of the concept as several *have* proposed it is that a  
> regional authority - a city, perhaps, or a consortium of ISPs, or  
> in the latest version of the proposal I have seen the country of  
> Korea - gets a prefix, and sets up an arrangement. SOHOs that want  
> to multihome within its territory are able to get small (/48? /56?)  
> prefixes from it, and providers that deliver service in the area  
> may opt in to supporting such SOHO prefixes.


> Whenever I have talked about the model with an ISP, I have gotten  
> blasted.

Well, the way you outline above isn't the only way to do aggregation  
on something other than provider. A while back I worked on this, see  

The idea is that a border router within an ISP/carrier network no  
longer holds a full copy of the global routing table, but only  
carries a subset. The AS as a whole still has a full view of the  
entire table, but aggregates make packets flow to a router that holds  
the appropriate part of the global routing table, and then that  
router hands the packets off to the right neighboring AS.

The aggregates are only used within the AS so there is no free  
transit. Obviously it works best if there is interconnection in the  
metro area in question, but it can also be made to work without dense  

Based on NANOG shim6 feedback and the push for IPv6 PI in the RIRs, I  
think it's time to really look at this and/or other non-traditional  
ways to aggregate. Apart from traffic engineering (which should be  
solvable) the main problem with shim6 is that it doesn't give users  
provider independent address space, and it's becoming pretty clear  
that many users REALLY want this, not withstanding all the IETF  
efforts to make renumbering easier.

Some sort of non-provider aggregation would allow portable address  
space for end-users without starting a time delayed meltdown of the  
global routing table. Another advantage is that such a mechanism  
makes it possible to start using aggregatable PI space as normale PI  
space immediately, and only implement aggregation in individual ASes  
(no coordination necessary) as the size of the routing table increases.

I dropped this approach 2.5 years ago when it turned out that there  
was no support for it in the multi6 working group, but the heavy  
criticism of shim6, the push for PI in IPv6 and the fact that  
geographic aggregation keeps coming up from time to time suggests  
that it's probably not a bad investment of time for the IETF to look  
at this and see if there's something there. Maybe in the form of a BOF?


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