For decentralized compute users and distributed ml practitioners

Untangle NAT port forwarding and c10d rendezvous timeouts on TensorDock VMs.

Verify whether torchrun workers failed during initial TCPStore handshake, ephemeral port negotiation, or KVM hypervisor PCIe passthrough resets.

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Replay a resolved TensorDock multi-node incident

Upload your log file. Review the selected evidence and masking, then run diagnosis. Keep the original log for any follow-up questions.

Before uploading, review cloud data handling and local options.

training_logs.txt

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Up to 50 diagnoses a day for 30 days. Verify your work email to activate an eligible company evaluation, then replay a resolved incident and compare the evidence and next steps with your team's confirmed cause.

What a useful evaluation should establish

Establish whether network rendezvous failed at the initial port-forwarding layer or during dynamic NCCL socket peer exchange.

Use Denpex alongside your existing telemetry tools to investigate submitted incident evidence. With monitoring configured on a supported plan, detected failures can trigger alerts and an automatic diagnosis from the captured evidence.

Inside Denpex

See the evidence, not just the claim

Follow the causal chain, inspect the quoted evidence and prepare the next handoff. These actual product captures use founder-account examples and the VS Code extension, with the source identified under each image. Open a capture to inspect it at full size.

Denpex founder-account example: a causal graph connects an Xid 48 ECC event to a rank exit and downstream collective failures, with quoted evidence for each stage. — Live founder-account capture from the bundled NCCL/ECC example. Follow the hardware event, rank exit and downstream symptoms with a supporting log quote at each stage.Inspect original image

Denpex hardware handoff summary asks the operator to capture diagnostic evidence and verify RMA eligibility with the vendor. — Actual hardware handoff summary from the same founder-account example. Capture diagnostic evidence before an approved reset, then confirm RMA eligibility with the vendor.Inspect original image

Denpex historical example says a collective timeout does not establish the initiating rank, cause or failure domain and requests distinguishing evidence before a remedy. — Founder-account example restored from history. The original timeout remains unattributed, and the UI keeps the missing-evidence assessment visible.Inspect original image

Denpex VS Code extension displaying a bundled OOM-before-NCCL example, matched log evidence, verification guidance and an investigation handoff. — Actual VS Code extension capture of the bundled OOM-before-NCCL example. Review matched log evidence, verification guidance and the investigation handoff without leaving the editor.Inspect original image

Failure Signature Triage

TensorDock - Observed Runtime Evidence

Read TensorDock documentation

Incident pattern summary

A distributed job across two TensorDock VMs passes the MASTER_PORT=29500 TCPStore handshake, then fails 60 seconds later with NCCL socket connection refused. Because NCCL opens dynamic ephemeral ports outside the forwarded port range, workers cannot establish direct data rings without an overlay mesh or dedicated public IP.

Terminal traceback excerpt (TensorDock)

[E socket.cpp:957] [c10d] The client socket has timed out after 600s while trying to connect to (203.0.113.45, 29500).
torch.distributed.DistNetworkError: The client socket has timed out after 600s while trying to connect to (203.0.113.45, 29500).
tensordock-vm-2:1092:1108 [0] NCCL WARN Connect to 192.168.122.14<38912> failed : No route to host

Recommended verification flags

Set these environment flags in your training container or launch script to capture high-resolution collective logs:

NCCL_DEBUG=INFONCCL_SOCKET_IFNAME=wg0NCCL_IB_DISABLE=1TORCH_CPP_LOG_LEVEL=INFO

Diagnostic Scope Boundary

Denpex cannot provision dedicated IPv4 addresses or configure WireGuard tunnels on TensorDock instances. The evaluation pinpoints the exact network layer where multi-node communication broke down.