Spanning Tree Port State

This theme is the per-port forwarding state assigned by Spanning Tree, or its RSTP/MSTP successors — disabled, blocking, learning, or forwarding — along with the path-cost value used to calculate which ports get which state. A port stuck in blocking when it should be forwarding is a common cause of traffic that unexpectedly stops flowing through what looks like a healthy physical link, so admins check port state first when troubleshooting a working-cable-but-no-traffic symptom. Adjusting a port's path cost lets an admin deliberately steer which redundant link Spanning Tree prefers, useful when the network's default cost calculation, based on port speed, doesn't match the actual preferred topology.