NCCL RoCE GID Read Failed (Invalid argument)
NCCL fails to read the RoCE GID on containerized/macvlan setups because GID iteration starts at index 0 where leading entries are all-zero, returning EINVAL.
NCCL fails to read the RoCE GID on containerized/macvlan setups because GID iteration starts at index 0 where leading entries are all-zero, returning EINVAL.
What this failure is
NCCL RoCE GID Read Failed (Invalid argument) is a Communication failure seen during ML training runs. NCCL fails to read the RoCE GID on containerized/macvlan setups because GID iteration starts at index 0 where leading entries are all-zero, returning EINVAL. Common tags: Nccl, Roce, Gid Index, Macvlan.
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Why it happens (the mechanism)
GID iteration starts from index 0. Macvlan/virtual interfaces have all-zero GIDs at indices 0-3, valid entries start at 4. Reading gid_attrs on a zero-GID returns EINVAL. Taken together, these mechanisms explain why the failure is reproducible, why it tends to surface on specific workloads or scales, and why generic mitigation attempts often fall short without addressing the underlying cause.
What you'll observe
- NCCL init aborts on Kubernetes pods with RDMA
- Happens with macvlan sub-interfaces or virtual NICs
- Connection abort during communicator setup
Common symptoms and what they mean
| Symptom | Why it happens |
|---|---|
| WARN NET/IB: read failed in ncclIbRoceGetVersionNum: Invalid argument | GID iteration starts from index 0 |
| GID table has leading zero entries (indices 0-3) | macvlan/virtual interfaces have all-zero GIDs at indices 0-3, valid entries start at 4 |
| RoCE connection abort during init | Reading gid_attrs on a zero-GID returns EINVAL |
Which systems are affected
- Kubernetes pods with macvlan sub-interfaces
- RoCE HCAs with zero-GID leading entries
- VMs with dual/virtual NICs (hypervisor GID layout)
How to confirm this is the problem
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.
- ✓Reproduce the failure from a clean checkpoint/seed: the symptom must appear without warm-up state from a previous run.
- ✓Verified signal present: WARN NET/IB: read failed in ncclIbRoceGetVersionNum: Invalid argument
- ✓Verified signal present: GID table has leading zero entries (indices 0-3)
- ✓Verified signal present: RoCE connection abort during init
- ✓A targeted fix from the "How to fix it" section eliminates or substantially reduces the symptom within one validation pass.
The fix and the prevention pattern
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Install the free VS Code extensionNCCL errors in context
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Root cause
- GID iteration starts from index 0
- macvlan/virtual interfaces have all-zero GIDs at indices 0-3, valid entries start at 4
- Reading gid_attrs on a zero-GID returns EINVAL
The fix and how to prevent it
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