We have a 3560G switch that we are using on a ONS backbone. We have the last 16 ports running Trunked mode up to a 454 SONET ONS. These ports are currently connected to ML 1000 cards that control the IP portion of the SONET. I need to setup the spanning tree so that only one side of the SONET ring forwards and the other side is in blocking mode. How do I do this on the switch. I have spanning tree PVST enabled. What else do I need?
If you only want to prevent loop but don't care at which point it's done, then simply enabling spanning tree will be sufficient. But if you want to have control over your topology and decide yourself which port should be forwarding and which blocking, then you'll need to manually set root bridge and port cost in such way that spanning tree will put desired ports in blocking/forwarding mode.
Search CCO for "Understanding Spanning Tree".