RSTP : TC While timer

Unanswered Question
Jun 7th, 2007
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On this page :

we can read :

"When a RSTP bridge detects a topology change, these occur: It starts the TC While timer with a value equal to twice the hello-time for all its non-edge designated ports and its root port, if necessary...."

How should we understand "if necessary" ?



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If the topology change cause a new path to the Root Bridge, then it will be necessary for a RSTP to change it's root bridge on the switch. Consequently, if the Topology Change does not affect the path to the current RSTP Root Bridge, it will not be ncessary to change the root port.

I agree that the wording in the reference you gave is a bit confusing

An RSTP bridge does not flush entries containing MAC addresses which were learnt via the port that received the configuration message with the TC flag on.

The above reads like the TC While timer does not affect or change the port the TC message arrived on, if it is the Root Port, then the timer effectively does nothing to it.


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