Sunday, June 20, 2021

Growing Pains in Industrial Spanning Tree Loop

Industrial campus, loop architecture, 24x7x365, all Cisco, old MMF. It was originally 8 switches, about 80 nodes. Spanning Tree (Cisco PVSTP) handled everything fine. Switch maintenance, power maintenance, fiber problems were all tolerable because of the redundancy that a loop provides.

It has grown to ~40 switches, 500 nodes, in an ad-hoc manner. The loop has been expanded, and increased complexity, and we have learned that RSTP does not scale well. There were regular bridge loops. I enabled loop guard and aggressive UDLD, added costs to paths, but that introduces new problems, such as delayed BPDU causing shut interfaces, macflaps, and more.

Management agreed the old network needs to be rebuilt. This project starts... in 5 years... In the meantime, I need to stabilize this environment. I am considering:

a- break the loops - this is not ideal because obviously downtime on an upstream switch will take down all downstream, and there are some long daisy chains in this environment.

b- alternative to spanning tree - I have looked into some alternatives, most seem to start with a different topology.

Any experience or ideas are welcome and appreciated!

I am also having trouble finding consultants who can look me in the eye and speak with knowledge and confidence in this area. Can I ask for consultants in this sub? If not, please PM me



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