Actually this outage report is a good example of compounding systematic errors. A among the things that went wrong: incorrect and impossible packet sizes were d

Actually this outage report is a good example of compounding systematic errors. A among the things that went wrong: incorrect and impossible packet sizes were detected, the rule generator generated rules matching the impossible packet sizes, the human operator who looked at the rules and entered them in to the router didn't notice any problems, and finally the routers responded to the incorrect rules by starting to crash. Had any of these steps not gone wrong there likely would not have been an outage. It was a combination of failures that caused it.