<I'm mostly sitting this one out, guys and gals... Been there, done that, have *all* the T-shirts, way too many times... I know I should really just ignore Tim, sending him replies just keeps him going, but this one was too food to pass up. For now I'll be totally civil, and let Sean handle the ridicule and abuse approach... :-> From: Tim Bass (from cais.com) <cais@dune.silkroad.com> There are at least five hierarchical routing architectures that are not CIDR based To start with, CIDR is not a "routing architecture", it's an addressing scheme; routing architectures are pretty much orthagonal. I.e. you could run a hierarchical link-state system sort of like OSPF in the Internet with the exact same addressing as we have today (of course, you'd have to add more levels of areas to the protocol, etc). So, assuming you meant "five hierachical addressing schemes", could you enumerate them for the rest of us? I can think of only one addressing scheme which is really significantly different from CIDR (Landmark doesn't count, it's basically CIDR with diffuse boundaries), and that's Geographic. What is hard to understand is why men and women with intelligent brains believe that there is only 'one way, one religion' to do hierarchical routing. You need to distinguish between routing, and the addresing structure it uses. There are numerous ways to do the routing (i.e. the calculation of paths and/or routing table entries, such as destination-vector, link-state, etc), but there seems to be only one way to make the addressing work for very large networks, and that is to use the approach in CIDR. I am quite sure that the most vocal advocates of CIDR have read very little historical documents outside of the IETF RFCs. Oh, really? I guess I don't count as a very vocal advocate of CIDR... and I guess the same goes for Tony and Yakov. Hi guys! :-) I highly recommend some time spent in review of the principals of hierarchical routing; graph theory; queuing systems; dynamic programming and others as well as the marginalia of journal articles on the subject. Queueing systems aren't much use for this aspect of routing. Noel