16 vs 32 bit ASNs [Re: BBC does IPv6 ;) (Was: large multi-site enterprises and PI]

Mon Nov 29 19:40:31 UTC 2004

On Mon, 29 Nov 2004, Owen DeLong wrote:
>> Also, with 32bit ASN's, also expect upto 2^32 routes in your routing
>> table when each and every ASN would at least send 1 route and of course
>> there will be ASN's sending multiple routes.
>
> Only if EVERY ASN were allocated and active.  You and I both know this
> doesn't begin to approach reality.  Slightly more than half of current
> ASNs are actually in the routing table.  The ASN issuance rate is not likely
> to go up simply because we go to 32 bit ASNs.  Probably we are really talking
> about a need for 20 bit ASNs or so, generally, but, 32 bits is a much more
> convenient boundary for lots of code implementations and lots of hardware,
> so, 32 bits is the chosen number for the sake of simplicity.

Of course, every ASN would not be active.  But if we'd have 32 bit 
ASNs, there would be "no need" (or so folks would argue) to be strict 
in the policies -- everyone and their uncle could have one.  Folks 
could even get ones for their homes, theis SOHO deployments, or their 
3-person, on-the-side consulting companies.  And logically, each of 
these should have their own PI prefixes and a slot in the global 
routing table.

Scalable? NO.  Not just the number of routes, but also the churn those 
routes would make.. Oh god.

It's better to try to stick to 16 bit ASNs for now, and make stricter 
policies and reclaim the space if needed.

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings