Congestion Notification Packets are control-feedback messages used by RoCEv2 congestion-management mechanisms. When a receiving endpoint observes an ECN-marked packet, it generates a CNP toward the sender, instructing the transmitting endpoint to reduce its transmission rate. Losing these packets would delay congestion response and allow queues to continue building.

Cisco's validated RoCEv2-over-VXLAN design explicitly states that CNP packets use DSCP 48 and are classified into a high-priority queue . In Cisco's example, ordinary RoCEv2 traffic is mapped to QoS group 3, while CNP is mapped to QoS group 7. Cisco further states that the high-priority classification ensures that CNP packets are not dropped in the network.

Traffic shaping in option A would regulate CNP transmission rather than guarantee timely feedback. Option C places CNP in the same potentially congested queue as the data traffic that generated the congestion, defeating the purpose of reliable feedback. Option D is also incorrect because PFC is intended to protect a lossless data priority; CNP itself should be forwarded through a high-priority queue and should not depend on pause behavior.

Study Guide Reference: AI Infrastructure Deployment and Data Management — RoCEv2, ECN, CNP, QoS classification, and congestion management.

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