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Routing vs Switching (was Re: Another UUNET Explanation)
Alex Rubenstein <email@example.com> writes: > Ummm.. Maybe you are missing my point. Those of us that do not have > bottomless pockets to pay for a "EVERY ROUTET HAS A CONNECTION TO EVERY > OTHER ROUTER (VIA PPP -- added by me). Hmmm... a router that is connected to every other router via PPP has precisely the same problems as a router connected to every other router by PVCs using some kind of CBR-like service. If I had bottomless pockets I would still design a maximally hierarchical network. Some routers would be connected to long-haul point-to-point circuits. Other routers would talk either via some sort of LAN thing or if money were no object, probably via POSIP. The idea would be to create a tree-like fan-out from the "backbone" routers (the ones with the long-haul circuits) to the "customer aggregation" routers, aggregating traffic and reachability information upwards from many customers towards a set of crunchy boxes with relatively few (but very fat) interfaces. The idea is to conserve the amount of work any given router has to do with respect to convergence, since that's a poorly-scalable hot-spot. In the past the hot-spot may have been the amount of traffic through a box, such that so few fat interfaces could be used that it was economically compelling to move that particular load into some sort of L2 switch and take the lumps wrt inherent routing scalability problems and the lack of conservation of configuration effort. Since there are existence proofs that this hot spot is now no longer economically insurmountable, and some much crunchier boxes are on the near horizon, the argument for using smart L2 fabrics at all is becoming weaker. > I never said it was the catch all / fix all. But, it is cheaper, and n our > environment, works well and affordably. Backhoes can only do so much > damage, and that is why one has backup ISDN or some > other means. ISDN does a lousy job of backing up 140Mbps worth of traffic... However, as I said in another message, I buy the argument that tariffs and vendor pricing (particularly cost/port for low-speed interfaces, modulo things like the CT-3 card) make fast-packet L2 fabrics attractive. What I don't understand is the "why route when you can switch?" assertion, and I'd love someone to explain it to me in simple terms. > In a high scale network (like BlueBlue Net), they have > several DS3 Frame Relay trunks leaving each PoP, so that > dismisses the backhow bit also. Something has to do the converging when the underlying physical topology changes, no? Sean. (out-of-touch former network hack) - -- Sean Doran <firstname.lastname@example.org> "Boy, you obviously don't have a clue!" -- Chad Skidmore, Datasource L.L.C.