| How did you configure those three concentrators? The layout that comes
to mind does have a single point of failure...
Sure, it's easy to do this with two concentrators. Connect them via
the A/B ports (so they are on the dual ring). I assume you have two
FDDI adapters per 6000... Connect one to the first concentrator, one
to the second. Repeat for each 6000.
If one concentrator dies, the other one is left and the dual ring is
wrapped. If a dual ring cable breaks, the ring wraps but everything
remains accessible. If an M-S cable breaks, the other adapter can
still reach the other concentrator.
You shouldn't add extra levels to the hierarchy without a reason. In
small networks, it's perfectly reasonable to have a couple of
concentrators on the dual ring and everyone else connected straight to
those. The reason for going with multiple concentrator levels (a
couple on the trunk ring and a lot more on the level below) is that
your network is large enough that you don't really want so many
concentrators on the dual ring (say, order of 10 concentrators or more)
or the distances require more intermediate fan-out points, or the
structured wiring design calls for the additional level.
paul
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