200-150 · Question #123
What is the default bridge ID priority for Rapid PVST+?
The correct answer is B. 32769. This question tests knowledge of the default bridge ID priority value used in Cisco's Rapid PVST+ spanning-tree implementation.
Question
What is the default bridge ID priority for Rapid PVST+?
Options
- A128
- B32769
- C32768
- D4096
How the community answered
(36 responses)- A3% (1)
- B92% (33)
- C6% (2)
Why each option
This question tests knowledge of the default bridge ID priority value used in Cisco's Rapid PVST+ spanning-tree implementation.
128 is the default spanning-tree port priority value, not the bridge ID priority.
In Rapid PVST+, Cisco uses the extended system ID feature, which appends the VLAN ID to the base bridge priority. The default base priority is 32768, and for VLAN 1 (the default VLAN), the VLAN ID of 1 is added, resulting in a default bridge ID priority of 32769. This extended system ID mechanism allows each VLAN to have a unique bridge ID without requiring manually different priorities.
32768 is the base priority before the extended system ID (VLAN ID) is added; once VLAN 1's ID is appended, the effective value becomes 32769.
4096 is the increment unit used when manually configuring bridge priority values; it is not the default priority.
Concept tested: Rapid PVST+ default bridge ID priority with extended system ID
Source: https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9600/software/release/17-1/configuration_guide/lyr2/b_171_lyr2_9600_cg/configuring_rapid_pvst.html
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