Examkin

Question

Difficulty: EasyRapid PVST+ Spanning Tree Protocol Operations and Roles

A network engineer wants to configure a switch as the primary root bridge for VLAN 20 using Rapid PVST+. What is the lowest valid base bridge priority value that can be specified in the configuration command before the System ID Extension is added?

  1. 0Answer
  2. B
    1
  3. C
    20
  4. D
    4096

Answer

The lowest valid base bridge priority value is 0.
In Rapid PVST+, the base bridge priority is configured in increments of 4096 due to the 12-bit System ID Extension field. The valid range for base priorities is 0 to 61440 in steps of 4096. Therefore, 0 is a valid value and represents the lowest possible base priority.

Step-by-Step Solution

1
Identify the Rapid PVST+ bridge priority configuration rules.
Rapid PVST+ uses the 802.1t System ID Extension, which forces base bridge priority values to be configured in increments of 4096.
The 16-bit Bridge Priority field is divided into a 4-bit Priority field and a 12-bit System ID Extension (VLAN ID).
2
Determine the range of valid base priority values.
Valid base priority values are 0, 4096, 8192, 12288, ..., 61440.
The 4-bit priority multiplier allows values from 0×40960 \times 4096 up to 15×409615 \times 4096.
3
Select the lowest valid configured value.
The minimum allowed base priority is 0 (which results in a total priority of 0+20=200 + 20 = 20 for VLAN 20).
0 is the lowest multiple of 4096.

Key Concept

Rapid PVST+ Bridge Priority and System ID Extension Calculation
Rate this question

Topics

Rapid PVST+ Spanning Tree Protocol Operations and Roles

More questions from this topic