ibv_rc_pingpong: Failed to modify QP to RTR errno 110 Connection timed out

An RDMA queue pair could not transition to Ready-To-Receive, so the connection never established. On RoCE this is nearly always a GID index or MTU mismatch between the two endpoints; on InfiniBand it points at the subnet manager not having configured the path. This entry explains how to confirm the cause, apply the fix, and separate it from adjacent infiniband failures.

Quick answer

ibv_rc_pingpong: Failed to modify QP to RTR errno 110 Connection timed out means An RDMA queue pair could not transition to Ready-To-Receive, so the connection never established. On RoCE this is nearly always a GID index or MTU mismatch between the two endpoints; on InfiniBand it points at the subnet manager not having configured the path. Preserve the first preceding error, then run the targeted control below.

Symptom: ibv_rc_pingpong: Failed to modify QP to RTR errno 110 Connection timed out
Root cause: An RDMA queue pair could not transition to Ready-To-Receive, so the connection never established. On RoCE this is nearly always a GID index or MTU mismatch between the two endpoints; on InfiniBand it points at the subnet manager not having configured the path. The decisive evidence is the first log line that precedes "ibv_rc_pingpong: Failed to modify QP to RTR errno 110 Connection timed out" and differs from a healthy run.
Recommended fix: on RoCE, confirm both endpoints use the same GID index and RoCE version, show_gids on each host, and set NCCL_IB_GID_INDEX to match. Confirm MTU agrees on both sides.
How Denpex helps: Denpex investigates ibv_rc_pingpong: Failed to modify QP to RTR errno 110 Connection timed out 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.

Communication#infiniband#rtr#connection#timed#out#errno

What this failure is

The literal signature is "ibv_rc_pingpong: Failed to modify QP to RTR errno 110 Connection timed out". It is a communication failure associated with InfiniBand, RoCE, and RDMA queue pairs. The line identifies the failing operation or subsystem, while the surrounding evidence decides whether it is the initiating fault or a downstream symptom.

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Why it happens (the mechanism)

An RDMA queue pair could not transition to Ready-To-Receive, so the connection never established. On RoCE this is nearly always a GID index or MTU mismatch between the two endpoints; on InfiniBand it points at the subnet manager not having configured the path. 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.

What you'll observe

The workload stops or loses forward progress after emitting "ibv_rc_pingpong: Failed to modify QP to RTR errno 110 Connection timed out".
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.

Common symptoms and what they mean

Symptom	Why it happens
ibv_rc_pingpong: Failed to modify QP to RTR errno 110 Connection timed out	An RDMA queue pair could not transition to Ready-To-Receive, so the connection never established. On RoCE this is nearly always a GID index or MTU mismatch between the two endpoints; on InfiniBand it points at the subnet manager not having configured the path.
The same operation fails at a consistent stage of InfiniBand, RoCE, and RDMA queue pairs.	The decisive evidence is the first log line that precedes "ibv_rc_pingpong: Failed to modify QP to RTR errno 110 Connection timed out" and differs from a healthy run.
The first related warning appears before the final exception and names the causal subsystem.	A nearby failure remains a competing hypothesis until a control separates configuration, capacity, transport, and hardware causes.
A known-good control changes one variable and either reproduces or clears the failure.	An RDMA queue pair could not transition to Ready-To-Receive, so the connection never established. On RoCE this is nearly always a GID index or MTU mismatch between the two endpoints; on InfiniBand it points at the subnet manager not having configured the path.

Which systems are affected

InfiniBand, RoCE, and RDMA queue pairs
production-shaped multi-accelerator workloads
containerized and bare-metal deployments of the same stack

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.

✓Find the first occurrence of "ibv_rc_pingpong: Failed to modify QP to RTR errno 110 Connection timed out" and preserve at least 100 lines before it.
✓Identify which rank, node, device, or process emitted the first related warning.
✓ibstat / ibv_devinfo, the port must be ACTIVE with a valid LID (InfiniBand) or a valid GID (RoCE). On IB, check that a subnet manager is running (sminfo). Test the raw path with ib_write_bw between the two hosts before blaming the application.
✓Repeat the same input after the targeted change and require the signature to disappear.
✓Resume from job start only after the control passes.

Root cause

An RDMA queue pair could not transition to Ready-To-Receive, so the connection never established. On RoCE this is nearly always a GID index or MTU mismatch between the two endpoints; on InfiniBand it points at the subnet manager not having configured the path.
The decisive evidence is the first log line that precedes "ibv_rc_pingpong: Failed to modify QP to RTR errno 110 Connection timed out" and differs from a healthy run.
A nearby failure remains a competing hypothesis until a control separates configuration, capacity, transport, and hardware causes.

The fix and how to prevent it

Searchable error signature

search key

ibv_rc_pingpong: Failed to modify QP to RTR errno 110 Connection timed out

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.

The fix and the prevention pattern

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Why the recommended fix works

on RoCE, confirm both endpoints use the same GID index and RoCE version, show_gids on each host, and set NCCL_IB_GID_INDEX to match. Confirm MTU agrees on both sides. This changes the condition in the causal diagnosis instead of hiding the outer exception. The repeated control proves ownership before recovery from job start.

Code examples

snippet

# Preserve evidence before restarting
NCCL_DEBUG=INFO NCCL_DEBUG_SUBSYS=INIT,NET,COLL torchrun train.py
ibstat
ethtool -S <interface>

# Find the exact signature in the complete log
rg -n -F -- "ibv_rc_pingpong: Failed to modify QP to RTR errno 110 Connection timed out" <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.

Best practices by model family

Model / Stack	Recommendation	Notes
First response	Preserve the first failure	Keep the context before "ibv_rc_pingpong: Failed to modify QP to RTR errno 110 Connection timed out" so aggregation does not erase causality.
Confirmation	Change one variable	Use a known-good node, rank, input, or configuration as the control.
Recovery	Resume from job start	Resume only after the literal signature no longer appears in the same control.

With the fix vs without the fix

Dimension	With the fix	Without the fix
Evidence	First preceding error and one controlled comparison	Only the final aggregated exception
Fix	on RoCE, confirm both endpoints use the same GID index and RoCE version, show_gids on each host, and set NCCL_IB_GID_INDEX to match. Confirm MTU agrees on both sides.	Retrying the unchanged workload
Exit criterion	"ibv_rc_pingpong: Failed to modify QP to RTR errno 110 Connection timed out" is absent in the repeated control	The job happened to run once

Diagnostic note

“Treat "ibv_rc_pingpong: Failed to modify QP to RTR errno 110 Connection timed out" as a search key and an investigation checkpoint, not as proof of every cause associated with the phrase. The high-value evidence is what changed immediately before it and whether the failure follows the workload, node, or configuration.”

Visual fingerprint

Decision path for ibv_rc_pingpong: Failed to modify QP to RTR errno 110 Connection timed out

literal error captured
        |
        v
find first preceding failure
        |
        v
run one known-good control
        |
        +-- follows workload --> inspect input or configuration
        +-- follows node ------> inspect hardware or platform
        +-- disappears --------> validate the targeted fix

The control separates workload, configuration, and node ownership before recovery from job start.

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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.

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Related failures to investigate next

Frequently asked questions

Questions engineers and on-call staff commonly ask about this failure.

What does "ibv_rc_pingpong: Failed to modify QP to RTR errno 110 Connection timed out" mean?

Is this line always the root cause?

No. It can be the direct failure or the point where an earlier failure becomes visible. The first preceding error and a controlled comparison decide which.

What should I collect before restarting?

Collect complete log context, the emitting rank or node, component versions, resolved configuration, and the diagnostic output shown above.

What is the fastest confirmation?

ibstat / ibv_devinfo, the port must be ACTIVE with a valid LID (InfiniBand) or a valid GID (RoCE). On IB, check that a subnet manager is running (sminfo). Test the raw path with ib_write_bw between the two hosts before blaming the application.

How do I prevent it from recurring?

pin NCCL_IB_GID_INDEX and the MTU in the job template; validate the fabric with perftest during node acceptance.

References

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