Yesterday I was testing the failover of redundant links between a 3550 and a 4507 core switch.
I had created a etherchannel made up of two fastethernet ports and one gigabit fiber port on the 3550. I made a corresponding etherchannel on the 4507. I attached all ports mentioned and all was well. I did a show etherchannnel summary on the 3550 and I could see that the fiber port was marked P and the two fastethernet ports were marked s.
I then thought I would test the failover. I pulled the fiber cable from the 3550 and about thirty seconds later the fastthernet cables started forwarding traffic. So far so good.5 minutes Later I put the fiber cable back into the 3550. The link light went green right away and about 1 minute later the phone started ringing off the hook. The network was down. I pulled all the cables from the 3550 and in about 30 seconds the network was back to normal.
OK, this is what I think happened and this is where I would like your ideas too. I think what happened was the fiber link only went unidirectional and we got a STP loop.
If thats what happened I want to deploy UDLD on the fiber ports I have on my 3550s and on the core.
What I dont see is the purpose for normal mode UDLD is if it does nothing if it detects unidirectional traffic, and the aggressive mode scares me becuase I know one day UDLC will detect a unidirectional port which really isnt unidirectional and shut down the port. But since I have no experience with UDLC, I guess what I am asking is if this protocol has worked for you and is worth deploying.
So in my case can I use UDLC on ports in a etherchannel if I decide to go with it?