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← Labs ← Chapter 5: PFC & ECNFix the PFC priority mismatch

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Fix the PFC priority mismatch

intermediate

Elapsed

00:00

Scenario

RDMA training traffic is dropping packets after a switch config migration. The team believes PFC is enabled on the DGX-facing downlink, but AllReduce latency is up 45% and retransmit/drop counters are rising on the host. Your task: 1. Confirm drops are occurring on the DGX NIC 2. Inspect swp1's PFC configuration, including the enabled priority 3. Cross-check that priority against the RoCE DSCP/priority mapping 4. Apply the RoCE QoS profile and commit the config 5. Verify PFC is on switch-priority 3 and NIC drops stop

Conditions

Packet drops confirmed on NIC
PFC priority field inspected
Priority mismatch identified
PFC reconfigured to priority 3
PFC verified with show dcb pfc

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Topology

Filled green circle = Active

Unfilled red circle = Down

Solid line = 400G link

Dashed line = degraded

Click a device node to open its terminal session

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