Today I learned misconfigurations suck

[archivalbackup]

Took me a few days to track down, but in the midst of configuring and troubleshooting a really complicated network transition to facilitate moving our entire datacenter to all new equipment (servers, san, switches) I ended up with a VPC link between the new Nexus switches and the old 6500 core that was loosing 20% of the traffic going across it.

Fast forward and somehow this worked just enough to make things work very poorly:
I missed the 'active' on the port channel after troubleshooting some links so one side was set to 'channel group 20' but neither static on, nor lacp. The other side was configured as active. The far side somehow the native vlan trunk on the 6500 port channel got cleared off, but was still on the interfaces and the Nexus VPC.

So on one side of the link it was an etherchannel with no mode with a trunk native vlan of 800, on the other side it was a etherchannel active with a trunk native vlan of 1 on the port channel, but because the portchannel failed to come up, the interface configuration native vlan was working, and due to the fact I put a bpdu filter on the links to isolate it from spanning tree I think I caused a nice little network loop.

Glad I got that figured out before the weekend.