Most of this post is off topic; the conclusion is not. On the afternoon of Martin Luther King Day, 1990, AT&T's backbone network slowed to a crawl. The cause: a patch intended to save time when a switch that had taken itself off line (a rare, but routine and almost imperceptible event) rejoined the network. The patch was flawed; a lock should have been taken one instruction sooner. Bell Labs had tested the daylights out of the patch by subjecting a real switch in the lab to tortuously heavy, but necessarily artificial loads. It may also have been tested on a switch in the wild before the patch was deployed throughout the network, but that would not have helped. The trouble was that a certain sequence of events happening within milliseconds on calls both ways between two heavily loaded switches could evoke a ping-pong of the switches leaving and rejoining the network. The phenomenon was contagious because of the enhanced odds of a third switch experiencing the bad sequence with a switch that was repeatedly taking itself off line. The basic problem (and a fortiori the contagion) had not been seen in the lab because the lab had only one of the multimillion-dollar switches to play with. The meltdown was embarrassing, to say the least. Yet nobody ever accused AT&T of idiocy for not first testing on a private network this feature that was inadvertently "designed to compromise" switches. Doug