When a non-root switch determines which interface will serve as its Root Port, it processes incoming Bridge Protocol Data Units (BPDUs) using a specific sequence of decision criteria. Place the steps taken by the switch in the correct operational order from first to last.
- 1Receive BPDUs on active interfaces and read the Root Path Cost advertised by neighboring switches.
- 2Add the local receiving interface's port path cost to the advertised Root Path Cost for each port.
- 3Compare the cumulative path costs across all candidate interfaces to identify the lowest path cost.
- 4Apply tie-breaker rules (lowest designated Bridge ID, then lowest designated Port ID) if cumulative costs are equal.
Answer
The correct sequence for Root Port selection is: 1) Receive BPDUs and read advertised Root Path Cost, 2) Add local interface cost to calculate cumulative path cost, 3) Select the port with the lowest total path cost, and 4) Use tie-breaker criteria (lowest designated Bridge ID and Port ID) if path costs are equal.
The Spanning Tree Protocol (STP) Root Port selection mechanism follows a strict decision hierarchy: receiving neighbor advertised path costs first, adding the local interface cost to calculate total path cost second, choosing the lowest total path cost third, and resolving any ties using designated Bridge ID and Port ID values last.
Step-by-Step Solution
Key Concept
Spanning Tree Protocol (STP) Root Port Decision Sequence