When using the RSTP protocol, and its related configuration information is shown in the figure. According to the command configuration, please point out that for instance 1, the role of the switch is:

Question

Options

• ARoot switch
• BNon-Root switch
• CSwitch
• DCan't judge

• A
  76% (22)
• B
  3% (1)
• C
  14% (4)
• D
  7% (2)

Explanation

In RSTP/MSTP, the root bridge for a given instance is determined by the lowest bridge priority. The configuration shown in the figure sets this switch's priority for instance 1 to 0 (or uses root primary, which assigns the lowest possible priority), making it the definitive root bridge - hence A is correct.

B (Non-Root switch) is wrong because a non-root switch would have a higher priority value than this one, and all its ports would have either designated or root-port roles, not the all-designated-ports pattern of a root bridge.

C (Switch) is not a valid spanning-tree role; every participating switch holds a specific role (root or non-root), so this option is meaningless in context.

D (Can't judge) is wrong because the priority configuration directly and unambiguously identifies the root - there is no missing information.

Memory tip: Think "lowest priority = highest authority." A bridge priority of 0 is the floor value, so any switch configured with priority 0 for a given instance automatically wins the root election. If you see priority 0 or root primary next to an instance, that switch is the root for that instance.

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