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Re: "Selfish Routing"
From: Mike Lloyd <drmike () routescience com>
Date: Sat, 15 Feb 2003 13:11:45 -0800




Stephen Sprunk wrote:
The problem is eliminating the possibility of a packet taking a "near
optimal" path from A to B, and then taking another "near optimal" path from
B back to A

I suspect this is impossible to fix while retaining hop-by-hop routing.

Looping does indeed present a problem. If you want all nodes to play the "near optimality" game, you have to move very slowly - if I choose you, then we need a sensible way to guarantee that you won't choose me at the same instant. A mechanism to do so will slow all decisions down, potentially beyond the point of usefulness. However, I don't quite get from this problem to a need to abandon hop-by-hop routing.

Paul Vixie wrote:
> i dunno, i don't think igrp would scale to the size of the internet.
> wasn't there a 1/(n^2) relationship between metadata size and
> network capacity as a function of total delay*bandwidth product
> in the whole system?

Combining the scale problem and the looping problem suggests optimization would fit most sensibly in an environment where the number of choices under consideration is small, and some loop-free properties already exist.

Such conditions happen to occur where autonomous systems meet, and especially for a stub AS. Careful inter-AS BGP optimization makes a good deal more practical sense than, say, hysterically self-reconfiguring OSPF.

I could observe that the edge of a BGP AS is also a place where money sometimes changes hands, but I wouldn't want to infect a nice academic discussion with anything too commercial :-)

Mike


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