Re: Resolving geo discussions

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

On maandag, apr 14, 2003, at 15:38 Europe/Amsterdam, Brian E Carpenter 
wrote:

> > What exactly do we want to be in this RFC?
>  think it needs to build on the observation that there is no congruence
> between network topology and geography to show that we have no way to 
> make
> geo addresses aggregate in practice. It doesn't need to be that long.
> But since it's an abstract "why this doesn't work" argument, I think
> it needs to be separate from any specific technical proposal.
I disagree. The whole point of this RFC would be to end the discussion. 
That's not going to happen by simply presenting one viewpoint. Either 
it needs to be an overview that lists all the arguments pro and con and 
possibly drawing some conclusions along the way, or if it only presents 
a single point of view it must get into the nitty gritty and not 
suffice with "I know someone in Jakarta who connects to Reykjavik so 
geo aggregation can't work".

Why don't we do some calculations to see how good or bad it can work?

For instance, even in a worst case scenario when distribution of 
interconnection is completely random, there is always some gain to be 
had: if there are m interconnects, having an aggregate point to one 
interconnect and then filter out all routes that are identical to the 
aggregate must save 1/m-th in the routing table size in all nodes 
except the one sourcing the aggregate.

If we accept some constraints, we can do much better. For instance, if 
we use a fully switched network (not inconceivable with MPLS) we can 
have one node that sources the aggregate and holds all more specifics, 
all other nodes only need the aggregate and the more specifics learned 
from the local interconnect, which is 1/m-th of all more specifics on 
average.

In a routed network, the gains aren't as big as all intermediate nodes 
need to know the more specifics for packets that may need to be routed 
through them, but some quick guestimates land around the 50% mark. 
That's 18 months according to Moore, which doesn't sound like much but 
1.5 years interest on the "aluminum factory" as one former boss used to 
call it (our new network cost the same as an aluminum factory (and 
probably used as much electricity too)) adds up to a substantial pile 
of change.