Taking out a network - Quickly

We killed our network in a very similar manner. Instead of taking the switch from a test lab, we pulled the switch from the replaced with newer equipment shelf.

When the switch was configured off the network, all the Vlan definitions were deleted because they were not needed on this new project. It was not noticed that the switch was in server mode.

When the switch was connected to the network all but two Vlans disappeared very quickly from the multitude of switches supporting the building effectively taking the network down instantaneously. The time to recover was about 40 minutes - first to find a copy of the Vlan database because it isn't part of the configuration time and then to reformat it so that it can be imported into the Cisco configuration.

Read more here.

Hat tip Eric at ACSG.