Connection reset by peer error 104 appears when a remote host forcibly closes an existing TCP connection, leaving the local endpoint unable to continue communication. This behavior often indicates network instability, protocol violations, or server-side enforcement of security policies.
Understanding the causes and troubleshooting techniques helps developers and operators resolve dropped sessions more quickly and design resilient services that handle abrupt disconnections gracefully.
| Error Name | Errno Code | Common Cause | Typical Fix Focus |
|---|---|---|---|
| Connection reset by peer | 104 | Remote side closed socket unexpectedly | Detect, retry, and tune timeout settings |
| Broken pipe | 32 | Writing to a closed socket | Ensure peer is alive before write |
| Network is unreachable | 101Missing route to destination | Check routing and interface configuration | |
| Connection timed out | 110 | No response within timeout window | Adjust timeouts, retry logic, QoS |
How Connection Reset by Peer Error 104 Manifests
Socket Behavior on Remote Closure
When a server or intermediate device sends a TCP RST frame, the local socket reports errno 104 to indicate that the connection was reset rather than closed normally. This can appear in logs, console output, or monitoring dashboards as a sudden disruption with no graceful shutdown sequence.
Applications that do not anticipate such resets may crash or propagate misleading errors, so handling this specific errno as a controlled condition is important for reliability.
Common Network and Protocol Triggers
Load Balancers and Proxies Forcing Reset
Load balancers or API gateways may terminate idle or misbehaving client connections and immediately send RST to the backend, producing error 104 on the application side. This behavior is typical when health checks time out or when connection pools are aggressively managed.
Understanding the policies of intermediary devices helps distinguish between expected cleanup and abnormal failure conditions.
Protocol Violations and Security Devices
Intrusion prevention systems, web application firewalls, or protocol parsers may reset sessions that appear malformed or suspicious. TLS handshake failures, invalid HTTP framing, or unexpected payload sizes can trigger resets at the network layer.
Reviewing security device logs in parallel with application traces clarifies whether the reset originates from protective measures or genuine endpoint faults.
Client and Server Side Diagnostics
Instrumenting Code to Capture Errno 104
Enabling detailed socket options, setting appropriate SO_KEEPALIVE, and logging getsockopt errors help identify patterns around connection resets. On the client side, wrapping I/O calls with structured error handling ensures that errno 104 is surfaced clearly rather than masked by generic exceptions.
Tracing the sequence of send, recv, and close operations around the reset event pinpoints whether the disruption occurs early in the handshake or after significant data exchange.
Server Logs, Capture Tools, and Correlation IDs
Server-side diagnostics should record peer IP, port, and protocol state when a reset is detected. Correlating these records with packet captures and request IDs across services reduces mean time to resolution.
Visualizing connection lifetimes on timelines highlights whether resets cluster around specific endpoints, regions, or deployment versions, guiding targeted fixes.
Reliable Networking and Operational Recommendations
- Enable and tune TCP keepalive to detect dead peers before application timeouts.
- Implement idempotent retries with capped attempts and jitter to avoid amplifying congestion.
- Synchronize timeout and backoff values between clients and servers to reduce mismatch resets.
- Instrument socket errors with structured context, including request IDs and peer metadata.
- Review intermediary device policies, such as load balancer timeouts and WAF thresholds, in coordination with application settings.
FAQ
Reader questions
Why does my service see connection reset by peer only under heavy load?
Under heavy concurrency, connection pools may exhaust available sockets, causing intermediaries to terminate idle or slow connections and generate errno 104 on dependent clients.
Can TLS configuration directly trigger errno 104 on some clients?
Yes, mismatched cipher suites, unsupported protocol versions, or certificate verification failures can cause the remote side to reset the connection instead of completing TLS negotiation.
Do cloud load balancers contribute to connection reset by peer errors in containerized environments?
Cloud load balancers with short idle timeouts may close connections that appear stalled, which containers perceive as a reset by peer if keepalive settings are not aligned with the platform behavior.
How can I differentiate between a legitimate reset and a transient network glitch?
By correlating timestamps across logs, tracing route changes, and applying consistent retry with exponential backoff, you can distinguish occasional network drops from systematic reset patterns.