What you need to know
Are the HPC VMs positioned to use Azure's RDMA fabric rather than only sharing ordinary Ethernet connectivity?
Potentially affected
Owners of RDMA-capable Azure HPC deployments checking InfiniBand placement and network addressing.
DSE recommendation
Map each communicating node to its actual scale set or availability set before changing MPI settings.
Source facts
Azure’s documented HPC RDMA path uses InfiniBand, not the ordinary Ethernet interface. VMs needing RDMA communication must share a scale set or availability set; a scale-set deployment requires one placement group for its InfiniBand communication. Microsoft reserves 172.16.0.0/16 for the RDMA network and warns against overlapping the virtual network with it. Appropriate InfiniBand drivers are also required. Microsoft Learn.
Applicability
Confirm the exact RDMA-capable VM size, supported operating system, driver stack, and deployment model. The source contains older platform examples; use its current linked size and image guidance when qualifying a new build. Do not infer fabric eligibility solely from successful ordinary network tests.
DSE recommendation
Map each communicating node to its actual scale set or availability set before changing MPI settings. Have the compute owner confirm the scale-set placement configuration and the network owner compare address ranges with the reserved fabric space. Resolve a placement or address-design mismatch through an approved deployment plan, preserving the application’s existing recovery path.
Verification
On designated test nodes, inspect the actual fabric interface and driver state, then exercise the intended multi-node workload. Capture placement identifiers, selected interface, and observed communication separately from an Ethernet reachability result. If the job still fails within a valid fabric boundary, pass that evidence to the MPI owner for library-specific investigation. Avoid changing several placement, driver, and runtime variables together without a way to attribute the result.
Official references
Microsoft Learn: Set up InfiniBand. Source reviewed September 9, 2026.
Review the official source
Set up InfiniBand on HPC VMs - Azure Virtual Machines - Azure Virtual Machines | Microsoft Learn · Verified September 9, 2026
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