Question 410
An infrastructure administrator receives the following incident: A rack's Ethernet switches have a functioning management plane but RoCE data links fail because PFC and ECN settings diverge across adjacent devices. Which measured result most directly proves that this specific problem is resolved?
Explanation
Correct Answer
This is the measurable acceptance result for the described case: A multi-hop transport test carries the expected workload with acceptable drops, congestion signals, and no uncontrolled head-of-line blocking. It validates the corrective operation (Verify consistent supported loss and congestion-control policy across the complete affected fabric, not only device reachability.) rather than a related but different system check.
Incorrect Answers
This observation would help verify a different incident: One leaf switch reboots repeatedly under load after maintenance, while its peer leaf remains stable and has a different firmware revision. It does not directly establish the required result for the current case: A multi-hop transport test carries the expected workload with acceptable drops, congestion signals, and no uncontrolled head-of-line blocking.
This observation would help verify a different incident: Network engineers push a switch OS update to all spine switches simultaneously, briefly removing every path for long-running distributed training jobs. It does not directly establish the required result for the current case: A multi-hop transport test carries the expected workload with acceptable drops, congestion signals, and no uncontrolled head-of-line blocking.
This observation would help verify a different incident: After a GPU tray replacement, CUDA kernels run normally but NCCL tests between certain device pairs fail with fabric or peer-access errors. It does not directly establish the required result for the current case: A multi-hop transport test carries the expected workload with acceptable drops, congestion signals, and no uncontrolled head-of-line blocking.