NCP-AIO Administration Practice Question
An AI operations engineer is preparing a DGX H100 system for a multi-node training workload. The engineer runs `nvidia-smi topo -m` and notices that GPU4 and GPU5 report a connection type of SYS, while all other GPU pairs show NV18. What is the most likely cause of this topology anomaly?
⚠ Common exam trap
The trap here is assuming that SYS is a normal topology state for some GPU pairs on an NVSwitch-equipped system, when it actually indicates a degraded or absent NVLink path.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
GPU4 and GPU5 are connected through the PCIe host bridge rather than the NVSwitch fabric, possibly due to a degraded or missing NVLink connection.
A healthy DGX H100 shows NV18 (NVLink 4.0, 18 links) for every GPU pair because all GPUs are connected through NVSwitch. A SYS entry for a specific pair means traffic between those GPUs falls back to the PCIe/CPU path, which severely reduces bandwidth and increases latency. This typically signals a hardware or cabling fault on the NVLink side that should be resolved before running distributed training.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The NVSwitch fabric is operating in a fallback mode that only activates when peer-to-peer traffic exceeds a threshold.
Why it's wrong here
NVSwitch does not operate in a threshold-based fallback mode. It provides full non-blocking GPU-to-GPU connectivity at all times when healthy. A SYS designation between two GPUs indicates the path does not use NVLink at all, which is inconsistent with a healthy NVSwitch fabric and rules out this explanation.
- ✗
GPU4 and GPU5 are configured in MIG mode, which forces inter-GPU communication over the PCIe bus.
Why it's wrong here
MIG mode partitions a single GPU into isolated instances and does not change the physical interconnect between two separate GPUs. Even with MIG enabled, inter-GPU communication paths remain governed by NVLink/NVSwitch topology. MIG would not cause a specific GPU pair to report SYS while others report NV18.
- ✓
GPU4 and GPU5 are connected through the PCIe host bridge rather than the NVSwitch fabric, possibly due to a degraded or missing NVLink connection.
Why this is correct
SYS indicates that communication between those two GPUs traverses the system's PCIe and CPU interconnect instead of the high-speed NVLink/NVSwitch fabric. On a DGX H100, all GPU pairs should normally show NV18 via NVSwitch, so this points to a degraded or missing NVLink path between GPU4 and GPU5 that must be investigated.
- ✗
GPU4 and GPU5 are reserved for display output, so the driver automatically disables their NVLink interfaces.
Why it's wrong here
DGX H100 systems are headless compute nodes and do not reserve GPUs for display output. NVLink interfaces are not disabled based on display usage, and the driver does not selectively turn off NVLink for a subset of GPUs in this way. This explanation does not account for the SYS connection type reported by the topology query.
Visual reference
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official NVIDIA exam blueprint
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