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Difficulty: EasyRapid PVST+ Spanning Tree Protocol Operations and Roles

A network administrator configures a Cisco Catalyst switch running Rapid PVST+ with the command `spanning-tree vlan 50 priority 8192`. What total bridge priority value will this switch include in its outgoing Bridge Protocol Data Units (BPDUs) for VLAN 50?

  1. 82428242Answer
  2. B
    81928192
  3. C
    3281832818
  4. D
    82028202

Answer

The total bridge priority included in BPDUs for VLAN 50 is 82428242.
In Cisco Rapid PVST+, the 16-bit Bridge Priority field is divided into a 4-bit configurable priority value (in increments of 4096) and a 12-bit System ID Extension representing the VLAN ID. When a base priority of 81928192 is configured for VLAN 50, the switch combines the base priority with the VLAN ID (8192+50=82428192 + 50 = 8242) to form the total bridge priority advertised in BPDUs.

Step-by-Step Solution

1
Identify the base bridge priority configured on the switch.
The configured base bridge priority is 81928192.
The CLI command explicitly sets the base priority to 81928192.
2
Determine the System ID Extension for the specified VLAN.
The System ID Extension is equal to the VLAN ID, which is 5050.
Rapid PVST+ uses the 12-bit System ID Extension field to encode the VLAN number into the Bridge ID.
3
Calculate the total bridge priority advertised in BPDUs.
8192+50=82428192 + 50 = 8242.
Total Bridge Priority = Base Priority + System ID Extension.

Key Concept

Rapid PVST+ Bridge ID Structure and System ID Extension
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Topics

Rapid PVST+ Spanning Tree Protocol Operations and Roles

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