NVLink 5 switch tray ASIC port link training failed signal integrity

An NVLink switch tray port failed link training, the physical layer could not establish a clean signal. On an NVL72-class rack this removes a path from the fabric, and collectives crossing it either fail or silently take a much slower route. This entry explains how to confirm the cause, apply the fix, and separate it from adjacent blackwell failures.

Symptom

NVLink 5 switch tray ASIC port link training failed signal integrity

Root cause

An NVLink switch tray port failed link training, the physical layer could not establish a clean signal. On an NVL72-class rack this removes a path from the fabric, and collectives crossing it either fail or silently take a much slower route. The decisive evidence is the first log line that precedes "NVLink 5 switch tray ASIC port link training failed signal integrity" and differs from a healthy run.

Recommended fix

fence the affected tray/port and drain jobs whose topology crosses it. A partially trained fabric produces slow, non-deterministic collectives that look like a software problem.

How Denpex helps

Denpex investigates NVLink 5 switch tray ASIC port link training failed signal integrity using the evidence you provide or your connected workload collects. Earlier rank, host or application evidence is needed to distinguish an initiating failure from a downstream report.

The literal signature is "NVLink 5 switch tray ASIC port link training failed signal integrity". It is a hardware failure associated with Blackwell, Grace Hopper, NVLink fabrics, and liquid cooling. The line identifies the failing operation or subsystem, while the surrounding evidence decides whether it is the initiating fault or a downstream symptom.

An NVLink switch tray port failed link training, the physical layer could not establish a clean signal. On an NVL72-class rack this removes a path from the fabric, and collectives crossing it either fail or silently take a much slower route. The failure becomes visible at this call site because the operation first requires the missing resource, valid state, healthy peer, or correct result. Earlier log lines and a known-good control carry more causal value than the final wrapper exception.

• The workload stops or loses forward progress after emitting "NVLink 5 switch tray ASIC port link training failed signal integrity".
• A retry on the same configuration reproduces the failure because the causal state has not changed.
• The outer framework exception can hide the rank, node, allocation, or dependency that failed first.
• Increasing timeouts or reducing workload size can suppress the symptom without correcting the cause.

• Blackwell, Grace Hopper, NVLink fabrics, and liquid cooling
• production-shaped multi-accelerator workloads
• containerized and bare-metal deployments of the same stack

Use this checklist to test the hypothesis against a small reproduction. No single line proves the root cause, so preserve the preceding events and compare one variable at a time.

• ✓Find the first occurrence of "NVLink 5 switch tray ASIC port link training failed signal integrity" and preserve at least 100 lines before it.
• ✓Identify which rank, node, device, or process emitted the first related warning.
• ✓"eye diagram closed" is a signal-integrity result, not a configuration one, check cable/connector seating, contamination, and bend radius on the named port. Compare error counters at both ends; a fault at one end only narrows it to that side.
• ✓Repeat the same input after the targeted change and require the signature to disappear.
• ✓Resume from latest checkpoint on unaffected topology only after the control passes.

• An NVLink switch tray port failed link training, the physical layer could not establish a clean signal. On an NVL72-class rack this removes a path from the fabric, and collectives crossing it either fail or silently take a much slower route.
• The decisive evidence is the first log line that precedes "NVLink 5 switch tray ASIC port link training failed signal integrity" and differs from a healthy run.
• A nearby failure remains a competing hypothesis until a control separates configuration, capacity, transport, and hardware causes.

NVLink 5 switch tray ASIC port link training failed signal integrity

Use this text as a lookup key in logs and upstream issue trackers. It is not presented as a captured customer log. Confirm the cause from your own preceding events, versions, configuration and the cited references.

fence the affected tray/port and drain jobs whose topology crosses it. A partially trained fabric produces slow, non-deterministic collectives that look like a software problem. This changes the condition in the causal diagnosis instead of hiding the outer exception. The repeated control proves ownership before recovery from latest checkpoint on unaffected topology.

# Preserve evidence before restarting
dmesg -T | grep -iE 'NVRM|Xid|AER|NVLink|ECC'
nvidia-smi -q
dcgmi diag -r 3

# Find the exact signature in the complete log
rg -n -F -- "NVLink 5 switch tray ASIC port link training failed signal integrity" <log-file>

Adapt the snippet to your framework. The same pattern holds for PyTorch Lightning, Hugging Face Trainer, DeepSpeed, Megatron-LM, and vLLM training wrappers. Where the wrapper exposes a config flag (for examplelr_scheduler_type in Trainer), prefer the flag over the imperative API to keep the schedule declarative and reproducible.

Select the traceback or open the failed terminal, then run Denpex locally to see the initiating rank, collateral failures, exact fix, and verification command without uploading the log.