200-301 · Question #1300
Refer to the exhibit. Which switch becomes the root bridge?
The correct answer is C. SW 3. In a Spanning Tree Protocol (STP) enabled network, the root bridge is elected by the switch with the lowest Bridge ID (BID), which is a combination of the bridge priority and MAC address. Based on the provided correct answer, SW3 must possess the lowest BID, making it the root br
Question
Exhibits
Options
- ASW 1
- BSW 2
- CSW 3
- DSW 4
How the community answered
(54 responses)- A6% (3)
- B11% (6)
- C80% (43)
- D4% (2)
Why each option
In a Spanning Tree Protocol (STP) enabled network, the root bridge is elected by the switch with the lowest Bridge ID (BID), which is a combination of the bridge priority and MAC address. Based on the provided correct answer, SW3 must possess the lowest BID, making it the root bridge.
SW1 would only be the root if it had the lowest BID, which is not the case given SW3 is the correct answer.
SW2 would only be the root if it had the lowest BID, which is not the case given SW3 is the correct answer.
The root bridge in an STP topology is determined by the lowest Bridge ID (BID). The BID is a combination of the configurable bridge priority (default 32768) and the switch's base MAC address. For SW3 to be the root bridge, the exhibit must have indicated that SW3 either has a lower configured bridge priority than the other switches, or if all switches are using the default priority, that SW3 has the numerically lowest MAC address among them.
SW4 would only be the root if it had the lowest BID, which is not the case given SW3 is the correct answer.
Concept tested: STP 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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