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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 this example, B has been elected as the designated bridge, and Port 2 on C is in the
blocking state. The election of B as the designated bridge is determined by the exchange of
BPDUs between B and C. B had a better BPDU than C. B continues sending BPDUs
advertising its superiority over the other bridges on this LAN. Should C fail 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.
NOTE: A port must continue to receive BPDUs advertising superior paths to remain in the blocking
state.
There are a number of circumstances in which STP can fail, mostly related to the loss of a
large number of BPDUs. These situations will cause a port in the blocking state to transition
to the forwarding state.
HP ProLiant BL e-Class C-GbE Interconnect Switch User Guide D-9
HP CONFIDENTIAL Codename: DeLorean Part Number: 263682-002 Last Saved On: 2/5/03 10:46 AM