NCA NVIDIA Networking & Interconnects 4

Question 1

Which congestion control algorithm does NVIDIA recommend for RoCE deployments to handle AI/ML all-reduce traffic?

Accepted Answer

ECN-based DCQCN

Answer

DCQCN (Data Center Quantized Congestion Notification) uses ECN marks to proactively rate-limit RoCE senders before queue overflow occurs.

Question 2

What is the role of the Subnet Manager (SM) in an InfiniBand fabric?

Accepted Answer

Initializes the fabric, assigns LIDs, and computes routing tables

Answer

The Subnet Manager discovers InfiniBand topology, assigns Local Identifiers (LIDs), and programs routing tables in all switches.

Question 3

What does SR-IOV provide when enabled on NVIDIA ConnectX NICs in a virtualized environment?

Accepted Answer

Direct hardware NIC access for VMs without hypervisor overhead

Answer

SR-IOV creates Virtual Functions (VFs) that give VMs direct hardware access to NIC resources, bypassing the hypervisor data path.

Question 4

In NVIDIA's BlueField DPU, what distinguishes it from a standard ConnectX SmartNIC?

Accepted Answer

Embedded Arm cores that run a full OS and offload host CPU networking tasks

Answer

BlueField DPUs include Arm processor cores capable of running a full Linux OS, enabling complete networking stack offload from the host CPU.

Question 5

What is the maximum NVLink bandwidth available between two H100 GPUs in the same SXM server?

Accepted Answer

900 GB/s bidirectional

Answer

H100 NVLink provides 900 GB/s total bidirectional bandwidth per GPU (18 NVLink 4.0 lanes × 50 GB/s each).

(NCA) NVIDIA-Certified Associate Practice Test