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Difficulty: EasyRapid PVST+ Spanning Tree Protocol Operations and Roles

A network administrator manually configures a switch running Rapid PVST+ with a base bridge priority of 28672 for VLAN 100. What total priority value will be transmitted in the Bridge Identifier (BID) within BPDUs generated for VLAN 100 on this switch?

  1. 28772Answer
  2. B
    28672
  3. C
    32768
  4. D
    32868

Answer

28772 is the total bridge priority advertised in the BPDUs for VLAN 100 because Rapid PVST+ adds the VLAN ID (100) to the configured base bridge priority (28672).
In Rapid PVST+, Cisco switches append the 12-bit VLAN ID (System ID Extension) to the 4-bit configurable base priority. Adding the VLAN ID of 100 to the base priority of 28672 yields a total priority value of 28772.

Step-by-Step Solution

1
Identify the base bridge priority and the VLAN ID.
Base priority is 28672 and VLAN ID is 100.
Rapid PVST+ uses the 802.1t System ID Extension mechanism.
2
Calculate total priority by adding the System ID Extension (VLAN ID) to the base priority.
28672+100=2877228672 + 100 = 28772
The 16-bit Priority field in the BID consists of a 4-bit Priority field (multiples of 4096) and a 12-bit System ID Extension field.

Key Concept

Rapid PVST+ System ID Extension and Bridge Identifier (BID) Calculation
Estimated Time:45s
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Topics

Rapid PVST+ Spanning Tree Protocol Operations and Roles

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