This is a core data center switch in a redundant pair, so there is a secondary. This is considered primary and has mostly fiber connection out to dozens of other distribution closets. It's an older design and isn't using routed ports to distribution layer, but individual layer2 vlans for each individual link and vlan interfaces. So it's layer3 routing on each link, but the port is still a switch port. So universal link detection (UDLD) is used just as a precaution. UDLD ensures there is two way communication to avoid spanning-tree problems that can happen when you have only one way communication.
Well the supervisor (brains, does everything) failed and the secondary took over just fine. But when the primary was repaired all the fiber links were showing down.
Every switch connected to this 6509, there was no link on the 6500 ports. Turns out UDLD had shut down the ports on the distribution switches. Very strange as the only way that could happen is if control plane was totally down but yet there was still link. So the 6500 couldn't respond to UDLD frames, the other side had link, as such it's going to err-disable the ports.
I'm thinking I should set up automatic recovery of UDLD after this, never seen it happen. It's like data plane was up, control plane non existent on 6500.
Well the supervisor (brains, does everything) failed and the secondary took over just fine. But when the primary was repaired all the fiber links were showing down.
Every switch connected to this 6509, there was no link on the 6500 ports. Turns out UDLD had shut down the ports on the distribution switches. Very strange as the only way that could happen is if control plane was totally down but yet there was still link. So the 6500 couldn't respond to UDLD frames, the other side had link, as such it's going to err-disable the ports.
I'm thinking I should set up automatic recovery of UDLD after this, never seen it happen. It's like data plane was up, control plane non existent on 6500.