A network administrator attempts to force Switch-B to become the primary Spanning Tree Protocol (STP) root bridge for VLAN 10 during an upcoming maintenance window. The administrator executes the CLI command `spanning-tree vlan 10 priority 61440` on Switch-B. After taking the existing core switch offline, host traffic experiences unexpected latency, and diagnostic logs reveal that Switch-C—which has a default configuration—was elected root bridge instead of Switch-B. Switch-C has an STP priority of 32768 for VLAN 10. Which of the following explains why Switch-C became the root bridge instead of Switch-B?
- Spanning Tree Protocol elects the root bridge based on the lowest priority numerical value, making Switch-C's default priority of 32768 preferred over Switch-B's priority of 61440.Cevap
- BSwitch-B requires a Layer 3 SVI interface configured on VLAN 10 to participate in STP root bridge elections across switch broadcast domains.
- CSwitch-B failed to propagate Bridge Protocol Data Units (BPDUs) to Switch-C due to an untagged native VLAN mismatch on the interconnecting trunk link.
- DSwitch-B experienced late collisions on its uplink interface, causing the switch to drop outgoing BPDUs before Switch-C could process them.
Cevap
Spanning Tree Protocol elects the root bridge based on the lowest numerical priority value. Setting Switch-B's priority to 61440 made it less preferred than Switch-C's default priority of 32768.
In Spanning Tree Protocol (IEEE 802.1D / 802.1w), the root bridge election selects the switch with the lowest Bridge ID, which is composed of the priority value and MAC address. Because the administrator set Switch-B's priority to 61440, Switch-C (with the default priority of 32768) possessed a lower priority value and was successfully elected root bridge.
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STP Root Bridge Priority Selection