Spanning tree melt down ?

I suspect we will learn more about what happened to Beth Israel Deaconess
Hospital's network than we've ever heard publically about any of
Worldcom's network problems. Dr. John Halamka has already publically
stated he intends to tell other hospitals what happened and how they can
avoid the same problem.

Hopefully it will be something along the lines of "complex layer 2
networks are fickle, and have vastly fewer mechanisms to implement
policy than are available at layer 3; networks that serve different
departments within the same organization are just as worthy of layer-3
policy boundaries as separate enterprises that have a need to keep
their networks distinct." Sometimes the router or firewall that
protects you from another department is just as valuable as the one
that protects you from "the outside."

Those of us who have been in the Ethernet-based exchange point
business are well-aware of the dangers of building complex layer 2
topologies, especially when a portion of the customer base adds to the
L2 fabric by fronting their router with an aggregation switch that is
just as likely as not to be connected to another customer's
aggregation switch without the first customer's knowledge ("we thought
they provisioned a router port on their side, really"). Everyone
claims to - and to be honest, many do - operate their L2 equipment
correctly, but (funny thing) problems still occur.

Administrative boundaries, and well-thought-out means of implementing
those boundaries at places where networks touch, are important.