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19 Spanning Tree Protocol
the BPDU guard functionality is applied, when a BPDU is received, the port becomes
inactive, instead of running as a Spanning Tree target port.
Ports put in the inactive status can be released using the
This lets them link up again with PortFast ports with the BPDU guard functionality applied,
and resume communication.
19.12.2 BPDU filter
(1) Overview
On ports with the BPDU filter functionality applied, BPDU sending and reception are
stopped. The BPDU filter functionality is applied to ports with PortFast set, for which a
terminal is connected and loops are known not to occur.
(2) Notes on BPDU filters
When the BPDU filter functionality is set for ports other than those with PortFast applied,
because BPDU sending and reception are stopped, communication is cut off until a
timer-based port status transition is completed.
19.12.3 Loop guard
(1) Overview
When a unidirectional link fault occurs, such as when a one-way line is cut, and BPDU
reception is cut off, a loop might have occurred. Loop guard functionality prevents these
kinds of loops from occurring.
The following figure shows the problems that occur during unidirectional link faults.
340
activate
operation command.
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