Thus spake "Pete Kruckenberg" <pete@kruckenberg.com>
http://www.scienceblog.com/community/article1018.html --- This might be easier to understand if it was more technical, but I'm only aware of a lot of disabled features on my routers that are supposed to in theory do some of these things.
And they're disabled because they often result in routing loops, usually transient but sometimes permanent. With very careful planning, you can create scenarios where these features help; however, it's usually cheaper to add capacity than to improve efficiency when you include engineering and operational costs.
Abstractions and analogies aside, is this really a problem, and is it really worth solving? Sounds like a lot of additional complexity for the supposed benefits.
Some carriers are solving this problem with MPLS-TE, but not the way the author suggests. Other than the MPLS-TE solution, I'm not aware of any ISPs that use congestion- or RTT-based routing. [E]IGRP is the only IGP with a mechanism to implement this on a packet level, and experience shows it is unstable in most topologies. S