moving to IPv6

Fri Nov 7 15:51:30 UTC 1997

On Fri, 7 Nov 1997, Karl Denninger wrote:

> Of course, then what happens is that you have to revoke the multiple ASNs
> that some providers have - which IMHO should NOT have been issued.
> 
> "Administrative convenience" isn't a valid reason to be issuing ASNs all
> over the place.  There is no *need* to do so - there may be a *want* to do
> so, primarily because people don't want to carry their own customer's
> traffic for the majority of the trip in even one direction (which IMHO is
> baloney, but heh, that's just my point of view).

The legitimate reason for multiple ASs is when separate parts of the 
network have very different routing.  For example, let's say a big 
company on a single continent has one prefix for their whole network.  
They then expand to another continent.  If they use address space under
that same prefix, they wind up either having the transcontinental link
large enough to support all of the transcontinental traffic for that
prefix, or they wind up routing traffic across a transcontinental link
and back when it didn't have to.  Now, if they get a different prefix for
the new continent, traffic will take the optimal path.

This is no different than inefficiencies caused by the current 
implementation.  Generally, traffic gets to the destination AS as quickly 
as possible and then finds its way to the destination host from there.  
However, there may be a shorter path involving a different entry point 
into the destination AS.

With the larger address space of IPv6, there is the capacity for an arbitrary
number of levels in the hierarchy.  Obviously, making use of those levels
to improve on the inefficiency noted above will require more routes to be
propagated, so there is a tradeoff.  I don't think we want either a routing
table contaning one route per AS nor do we want one containing every subnet
with each AS.  Ideally, we would choose some level of detail between those
extremes, using multiple routes per AS only where they actually improve
routing.

John Tamplin					Traveller Information Services
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