200-301 · Question #1466
Refer to the exhibit. Which switch becomes the root bridge?
The correct answer is B. SW 2. In Spanning Tree Protocol (STP), the root bridge is elected based on the lowest Bridge ID (BID), which combines the bridge priority and the switch's MAC address.
Question
Options
- ASW 1
- BSW 2
- CSW 3
- DSW 4
How the community answered
(26 responses)- A12% (3)
- B81% (21)
- C4% (1)
- D4% (1)
Why each option
In Spanning Tree Protocol (STP), the root bridge is elected based on the lowest Bridge ID (BID), which combines the bridge priority and the switch's MAC address.
SW1 would not be the root bridge if SW2 has a lower Bridge ID, which is the deciding factor in STP root bridge election.
The root bridge in Spanning Tree Protocol (STP) is determined by the lowest Bridge ID (BID). The BID consists of a configurable bridge priority (defaulting to 32768) and the switch's unique MAC address. Therefore, SW2 must have the lowest Bridge ID among the switches, either due to a lower priority value or, if priorities are default, the lowest MAC address.
SW3 would not be the root bridge if SW2 possesses a lower Bridge ID, irrespective of other switch configurations.
SW4 would not be the root bridge if SW2 has a lower Bridge ID, which takes precedence in the STP root election process.
Concept tested: Spanning Tree Protocol root bridge election
Source: https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/10556-16.html
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