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Appendix A. Troubleshooting STP
Spanning Tree Protocol Failure
A failure in the STA 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.
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.
9033691-01
Figure A-1. STP Loop
VH-2402-L3 Management Guide 179
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