You started this chapter knowing enterprise servers and switches. You now know:
- Why GPU training requires a fundamentally different network
- How the AllReduce synchronisation barrier creates the lossless requirement
- The four parallelism types and which ones generate external network traffic vs intra-node NVLink traffic
- Why RoCEv2 traffic is structurally low-entropy, what flowlets are, and why this makes ECMP fail for AI fabrics
- Why InfiniBand was adopted from supercomputing, and why RoCEv2 emerged as an alternative
- The evolution from NIC -> HCA -> DPU and what each adds
- How AMD Instinct GPUs use Infinity Fabric / xGMI for intra-node scale-up instead of NVLink, and why the external Ethernet fabric stays operationally the same
- The complete anatomy of a DGX H100 and why each component exists
- How the three networks of a DGX deployment connect and why they are separate
- Why the same ConnectX-7 NIC can connect to an InfiniBand fabric or an Ethernet fabric -- and what changes across the entire infrastructure when you make that choice
Everything that follows in this course -- PFC, ECN, congestion control, CLI diagnostics -- is about making the compute fabric work correctly. You now understand what you are protecting and why it matters.