Examkin

Soru

Zorluk: OrtaRapid PVST+ Spanning Tree Protocol Operations and Roles

A network administrator is configuring Rapid PVST+ on a Cisco Catalyst switch. The administrator intends for the switch to advertise a total Bridge Priority of 2053020530 for VLAN 5050 in its outgoing BPDUs to influence the Root Bridge election. Which priority value must be specified in the `spanning-tree vlan 50 priority <value>` command?

  1. 20480Cevap
  2. B
    20530
  3. C
    24576
  4. D
    16384

Cevap

The base priority value that must be configured is 20480.
In Cisco Rapid PVST+, the Bridge Priority is composed of a 4-bit Base Priority field and a 12-bit System ID Extension field containing the VLAN ID. The Base Priority must be configured as a multiple of 4096 (0,4096,8192,dots,614400, 4096, 8192, dots, 61440). When the command `spanning-tree vlan 50 priority 20480` is executed, the switch automatically adds the VLAN ID (5050) to the base priority (2048020480), producing a total advertised Bridge Priority of 2053020530.

Adım Adım Çözüm

1
Understand the Spanning Tree Bridge Identifier (BID) priority composition in Rapid PVST+.
Total Bridge Priority = Base Priority + System ID Extension (VLAN ID).
Rapid PVST+ uses 802.1t System ID Extension, allocating 4 bits for the base priority (in increments of 4096) and 12 bits for the VLAN ID.
2
Calculate the required base priority for VLAN 50 given a total priority of 20530.
Base Priority = 20530 - 50 = 20480.
Subtracting the VLAN ID (50) from the target total Bridge Priority yields the exact base priority.
3
Verify that the base priority is a valid increment of 4096.
20480 / 4096 = 5 (an exact integer multiple).
The Cisco IOS CLI accepts only values in increments of 4096 (e.g., 0, 4096, 8192, 12288, 16384, 20480, 24576, 28672, 32768).

Anahtar Kavram

Rapid PVST+ System ID Extension and Bridge Priority Increment Calculation
Bu soruyu puanla

Konular

Rapid PVST+ Spanning Tree Protocol Operations and Roles

Bu konudan daha fazla soru