Bill Manning wrote: Just for grins, how fast do the LAN interconnects need to be? A FDDI is about as fast as a single DS-3. So it makes little sense to connect mode than one DS-3 to a BB box, since there's no way to get that traffic thru a LAN to customer access boxes in the cluster! Ideally, the capacity of LAN *attachments* (not the total bandwidth of the LAN switch!) should be about the same as the capacity of backbone links, multiplied by the number of backbone links attached to each backbone router. Of course, there are tricks to partially offload traffic from the cluster's LAN (like connecting high-speed customers directly to backbone boxes, and arranging BB topology so the transit traffic won't cross the LAN -- this works in case of "duplicate" backbone). Anyway, that boils down to the LAN switch being the single point of failure. There's no reasonable way to do "parallel" LANs with load sharing, as the number of destinations in intra-POP traffic is relatively small. Aggregations makes things even worse. All in all, the backbone router should be scalable to the point that it does not need any clustering; and redundancy is provided by "internal" duplication. --vadim