Two-switch redundancy without STP: Two switches are connected with two crossover links for redundancy, but Spanning Tree Protocol (STP) is disabled. What will happen on this switched network?
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AThe routing tables on the switches will not update.
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BThe MAC forward/filter table will not update on the switch.
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CBroadcast storms will occur on the switched network.
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DThe switches will automatically load-balance between the two links.
Answer
Correct Answer: Broadcast storms will occur on the switched network.
Explanation
Introduction / Context:Layer 2 redundancy without loop prevention leads to switching loops. Spanning Tree Protocol (STP) is designed to detect and block redundant paths, preventing broadcast storms and MAC table instability.
Given Data / Assumptions:
- Two physical links between the same pair of switches.
- STP is explicitly disabled.
- Standard Ethernet switching behavior applies.
Concept / Approach:Without STP, frames can circulate indefinitely across redundant paths, especially broadcasts, multicasts, and unknown unicasts, causing exponential traffic growth (broadcast storms) and MAC table flapping.
Step-by-Step Solution:
Redundant links + no STP → a Layer 2 loop exists.Broadcast or unknown unicast frames are flooded on all ports.Frames loop back across the second link, are re-flooded, and repeat, overwhelming the network.Verification / Alternative check:Packet captures and switch CPU utilization during such misconfigurations reveal increasing duplicate frames and high utilization.
Why Other Options Are Wrong:Load balance automatically: L2 switches do not load-balance parallel links by default; STP blocks one. Routing tables: Pure L2 switches do not have L3 routing tables. MAC tables not updating: They will update, but flapping occurs because of looping frames.
Common Pitfalls:Assuming redundancy is always good; without loop prevention it is catastrophic at Layer 2.
Final Answer:Broadcast storms will occur on the switched network.