So excited to read these! The one which I'll always remember was back when I was working in support. A call came in from a customer with a fairly sizeable network freaking out about a full network outage. Jumping into the network we found all traffic being black holed. Following the routing it seemed like everything was being routed to their VMware cluster. Asking the usual questions, the customer confirmed they weren't using VM's for any type of routing. Logging into the VMware cluster, we identified the VM which all traffic was being directed to. Shutting down the VM resolved the issue and the entire network was restored. After discussing further with the customer, we found that the cause was that they had spun up GNS3 on a VM with a replica of their network. It ended up route poisoning the entire network. The customer was relieved and it became a good story for the pub. Tldr: Customer called in for support with a full network outage. The culprit was a GNS3 VM route poisoning the production network.
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