Determining the Root Port on Nonroot Switches

Determining the RP of a switch when show command output is available is relatively easy. As shown recently in Example 2-8, both show spanning-tree and show spanning-tree root list the root port of the local switch, assuming it is not the root switch. The challenge comes more when an exam question makes you think through how the switches choose the RP based on the root cost of each path to the root switch with some tiebreakers as necessary.

As a review, each nonroot switch has one, and only one, RP for a VLAN. To choose its RP, a switch listens for incoming hello bridge protocol data units (BPDU). For each received hello, the switch adds the cost listed in the hello BPDU to the cost of the incoming ...

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