Regionally aggregatable address space for multihoming

[Iljitsch van Beijnum <iljitsch@muada.com>]

Hi.

I guess I'll jump right in.

After reading "IAB/IESG Recommendations on IPv6 Address Allocations to 
Sites" it occurred to me that a way to keep the number of routes in the
routing tables down could be to use regionally aggregatable address space for
multihoming.

The idea is that routers on one end of the globe have little need to know
very specific routes to multihomed networks in some another part of the
world. For instance, a router on the US west coast doesn't need to know how a
network in Europe is connected. It should just send the packet to the
east. At some point, the packet would end up in the destination region, or as
close to the destination region as the originating network extends, and only
there the originating network would have to know where to send the packet
next.

Individual networks could implement filters in strategic places to keep the
specific routes for multihomed networks inside the proper region. There is no
requirement that networks use the same regional subdivision: a European
network may use regions that map to two countries, while another network that
has only a few points of presence in Europe may see the entire continent as a
region. Some networks may prefer to keep carrying all routes everywhere.

All networks announce their customer's routes everywhere, but peers simply
filter out these announcements on exchange points that do not fall within
their idea of the region. So our European network would normally only accept
routes to Dutch addresses in Amsterdam and Brussels (for backup) but the
other network only connects to the exchanges in London and Paris so it would
pick up the announcements for the Dutch multihomed address range there.

A further reduction of the routing tables could be possible by installing
exchange routers for regions at internet exchanges. The exchange router would
announce an aggregate for the region and all networks may send traffic to
that router. The exchange router holds all the more specific routes for the
aggregate and forwards the packets to one of the providers for the
destination network.

A problem with this is that all networks that have multihomed customers in a
region must connect to all the exchanges where the aggregate is announced.
All other default free networks have to connect to at least two of the
exchanges for that region. Exchange routers should be present outside as well
as within the region they service, for reasons of redundancy and because not
all networks are present in all regions.

The granularity of the address assignments has to be fairly fine, so that it
doesn't conflict with the hierarchical structure of any existing network. A
granularity of 1 to 10 million people to a region seems reasonable. (This
would mean large cities or small countries/states/provinces.) With
potentially 1% of the population being multihomed that would make for about
100k routes per region, so today's routers would be able to handle several of
those regions.

Iljitsch van Beijnum