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Zorluk: OrtaRapid PVST+ Spanning Tree Protocol Operations and Roles

A network engineer configures a Cisco switch running Rapid PVST+ to serve as the root bridge for VLAN 12. The engineer executes the global configuration command `spanning-tree vlan 12 priority 12288`. What total Bridge Priority value will be carried in the BPDUs transmitted by this switch for VLAN 12?

  1. 12288Cevap
  2. B
    12300
  3. C
    12300
  4. D
    12300

Cevap

12300
In Rapid PVST+, Cisco switches use the 802.1t System ID Extension, which split the 16-bit Bridge Priority field into a 4-bit Base Priority field (increments of 4096) and a 12-bit System ID Extension field carrying the VLAN ID. When `spanning-tree vlan 12 priority 12288` is configured, the total priority field transmitted in BPDUs is the sum of the base priority (1228812288) and the VLAN ID (1212), resulting in 1230012300.

Adım Adım Çözüm

1
Identify the configured base bridge priority value.
The base priority is configured as 12288 (a valid multiple of 4096).
STP base priority values must be specified in increments of 4096.
2
Identify the System ID Extension (VLAN ID).
The System ID Extension is 12 for VLAN 12.
Rapid PVST+ uses the 12-bit System ID Extension field in the Bridge Identifier to encode the VLAN number.
3
Calculate the total Bridge Priority transmitted in BPDUs.
Total Priority = 12288 + 12 = 12300.
The total priority contained within BPDUs is the sum of the configured base priority and the System ID Extension.

Anahtar Kavram

Rapid PVST+ System ID Extension and Total Bridge Identifier Priority Calculation
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Konular

Rapid PVST+ Spanning Tree Protocol Operations and Roles

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