A network engineer analyzes RoCEv2 traffic flows in an AI training cluster and notices that...

RoCEv2 transports the InfiniBand transport protocol over UDP/IP, allowing RDMA traffic to traverse Layer 3 networks. The RDMA transport layer preserves packet-level sequencing, reliability, and ordering semantics that are inappropriate for arbitrary IP fragmentation. Consequently, RoCEv2 traffic is designed to traverse the network without IP fragmentation, making option D the intended technical answer. NVIDIA documentation confirms that RoCEv2 places the InfiniBand transport protocol behind UDP and IP rather than using the native InfiniBand network-layer header.

A consistent end-to-end MTU is therefore essential in GPU fabrics. AI clusters commonly use jumbo frames, and every switch interface, port channel, Layer 3 interface, and server NIC along the path must support the configured packet size. Unexpected fragmentation is incompatible with the deterministic behavior required by high-performance RDMA workloads.

Option A identifies a general IPv4 consequence of setting DF—Path MTU Discovery can use DF—but it is not the fundamental RoCE transport requirement tested here. Option B is incorrect because DF does not classify packets as RDMA. Option C is also incorrect because ECMP path selection is normally determined by packet-header hashing; the DF flag does not force packets onto a single path.

Study Guide Reference: AI Infrastructure Deployment and Data Management — RoCEv2, MTU design, lossless transport, and high-performance Ethernet.

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