links on the blink (fwd)

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.