Spanning Tree Protocol

Troubleshooting STP

This section describes several troubleshooting tips.

Spanning Tree Protocol Failure

A failure in the STP generally leads to a bridging loop. A bridging loop in an STP environment comes from a port that should be in the blocking state, but is forwarding packets.

Figure D-6: Example of Spanning Tree Protocol failure

In the example, switch B has been elected as the designated bridge, and port 2 on switch C is in the blocking state. The election of switch B as the designated bridge is determined by the exchange of BPDUs between switches B and C. Switch B continues sending BPDUs advertising its superiority over the other bridges on the LAN. If switch C fails to receive these BPDUs for longer than the Max Age (default of 20 seconds), it could start to transition its port 2 from the blocking state to the forwarding state.

IMPORTANT: A port must continue to receive BPDUs advertising superior paths to remain in the blocking state.

D-8

Compaq ProLiant BL p-Class GbE Interconnect Switch User Guide