North American Network Operators Group
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Re: Sensible geographical addressing [Was: 16 vs 32 bit ASNs yadda, yadda]

  • From: Iljitsch van Beijnum
  • Date: Tue Nov 30 14:56:36 2004 
On 30-nov-04, at 16:29, Scott Morris wrote:
In the interconnected world, geography is very much irrelevant to best path
routing. It's all about speeds and feeds where a local-access T-1 is
obviously not preferable to a cross-country OC-3.
I have a very hard time seeing this as a realistic example in interdomain routing. BGP has no idea about link speeds. I've seen many occasions where BGP selects a path that is inferior because all the paths cross the same number of ASes and that's the extent of BGP's knowledge.

When looking at a small scale, you're right that network topology and geography are very different. For instance, I live in The Hague, which is in a very small country very close to a major international fiber hub (Amsterdam). This means that it's almost impossible for me to reach someone else in The Hague (or the world, for that matter) without going through Amsterdam. If you look at Holland as a whole, the picture is very different: the vast majority of traffic between any two points within the country stays within the country. If you look at a Western-European scale, there is almost no traffic that leaves the region. And in 10 years, I've never seen any traffic between two points in Holland go through Africa, Asia or South America.

This means that with geographic aggregation in effect, 90% of Dutch more specific routing information can be aggregated away elsewhere in Europe, 98% in North America and (possibly) 100% elsewhere in the world.

Yes, there will always be exceptions. When you have a million entries in the routing table, you don't worry about the 30000 special cases as long as you can get the 970000 simple cases right.

Another misconception: the aggregation doesn't have to line up with the fiber. If London needs two aggregates because one half is in the western hemnisphere and the other half is in the eastern hemnisphere, who cares? And it gets even better when you consider that an ISP will carry all of its customer routes everywhere anyway: there is no need for two peers to agree where the routing information for a certain geographic area is exchanged: peer A simply listens for the information in the location that it finds most suitable, and so does peer B. There is no requirement for this to happen in the same location, or in the "target area" itself.