What Does the Curl 35 Recv Failure Connection Reset By Peer Error Mean and How Can I Fix It?

Encountering the error message “Curl 35 Recv Failure Connection Reset By Peer” can be both perplexing and frustrating, especially for developers and IT professionals who rely on smooth, uninterrupted data transfers. This cryptic notification signals a disruption in communication between your client and the server, often halting the flow of information and complicating troubleshooting efforts. Understanding the underlying causes and implications of this error is crucial for anyone working with network requests, APIs, or web services.

At its core, this error reflects a scenario where the remote server unexpectedly terminates the connection while your client is still waiting to receive data. Such interruptions can stem from a variety of sources, including network instability, server-side configurations, or security protocols that abruptly sever the link. While the message itself is concise, the factors contributing to it are multifaceted, requiring a nuanced approach to diagnosis and resolution.

In the sections that follow, we will explore the common triggers behind the “Curl 35 Recv Failure Connection Reset By Peer” error, discuss how it impacts data transmission, and outline practical strategies to identify and address the root causes. Whether you’re a seasoned developer or new to network troubleshooting, gaining insight into this issue will empower you to restore reliable connections and maintain seamless communication with your servers.

Common Causes of Curl 35 Recv Failure Connection Reset By Peer

The “Curl 35 Recv Failure Connection Reset By Peer” error typically indicates that the remote server closed the connection unexpectedly while curl was trying to receive data. This disruption can be caused by various factors related to network configurations, server settings, or client-side issues.

One common cause is the server forcibly closing the connection due to perceived security threats or policy restrictions. For example, some servers implement firewalls or intrusion detection systems that automatically reset connections from clients exhibiting suspicious behavior. Additionally, server-side timeout settings may close connections if the client takes too long to respond or send data.

Network issues such as unstable internet connections or intermediate network devices (like proxies or load balancers) can also reset connections unexpectedly. These devices might drop packets or terminate sessions if they detect anomalies or if their internal resources are constrained.

Misconfigured TLS/SSL settings on either the client or server can lead to abrupt connection resets during handshake or data exchange. This is particularly common when there is a mismatch in supported protocols or cipher suites.

Client-side problems, such as incorrect curl command options, outdated curl versions, or operating system-level restrictions, can contribute to connection resets as well.

Troubleshooting Steps for Curl 35 Errors

When encountering this error, a systematic approach to troubleshooting can help identify the root cause:

Check Server Status: Verify that the server is operational and not undergoing maintenance or experiencing high load.
Test Network Connectivity: Use tools like `ping` or `traceroute` to ensure stable communication between the client and server.
Review Firewall and Security Settings: Confirm that no firewall rules or security appliances are blocking or resetting connections.
Update curl and Libraries: Ensure that curl and its underlying SSL/TLS libraries are up to date to avoid compatibility issues.
Inspect curl Command Syntax: Validate the correctness of the curl command, including headers, data payloads, and protocol specifications.
Enable Verbose Logging: Run curl with the `-v` or `–trace` options to gather detailed logs for analysis.
Test with Alternative Tools: Use other HTTP clients like `wget` or browser requests to determine if the issue is specific to curl.

Adjusting curl Options to Mitigate Connection Resets

Certain curl options can be modified to reduce the likelihood of connection resets or to better handle them when they occur. These adjustments help tailor the behavior of the client to accommodate server or network conditions.

Option	Description	Example Usage
–retry	Automatically retry failed connections a specified number of times.	curl –retry 3 https://example.com
–max-time	Set a maximum time allowed for the entire operation to prevent hanging.	curl –max-time 30 https://example.com
–tcp-nodelay	Disable Nagle’s algorithm to send packets immediately, reducing delays.	curl –tcp-nodelay https://example.com
–tlsv1.2	Force the use of TLS version 1.2 to match server requirements.	curl –tlsv1.2 https://example.com
–http1.1	Force HTTP/1.1 protocol if server does not fully support HTTP/2.	curl –http1.1 https://example.com

By experimenting with these options, users can often avoid connection resets caused by protocol mismatches or network timing issues.

Server Configuration Considerations

Servers may reset connections to protect resources or enforce policies. Understanding and adjusting server configurations can help prevent unexpected connection resets:

Timeout Settings: Servers often have timeouts for idle connections or slow clients. Increasing these limits can reduce premature resets.
Connection Limits: High load or connection limits might cause servers to drop new or existing connections.
TLS/SSL Protocols and Cipher Suites: Ensuring the server supports a range of secure protocols compatible with clients helps maintain stable connections.
Reverse Proxies and Load Balancers: Intermediate devices may impose their own connection limits or timeouts that affect client-server communication.
Security Modules: Tools like mod_security or fail2ban may reset connections perceived as malicious.

Collaboration between client and server administrators is essential to fine-tune these settings and maintain reliable connectivity.

Network Infrastructure Impact on Connection Resets

Network hardware and configurations between the client and server significantly influence connection stability. Several elements may cause connection resets:

Firewalls: Stateful firewalls may drop connections if they detect inactivity or unusual traffic patterns.
NAT Devices: Network Address Translation can interfere with session persistence, especially with long-lived connections.
Load Balancers: Improperly configured load balancers may reset connections during failover or maintenance.
ISP Policies: Some Internet Service Providers throttle or reset connections for certain traffic types or under heavy load.

Understanding the network topology and behavior is crucial for diagnosing and resolving connection reset errors.

Additional Diagnostic Tools and Techniques

Beyond curl’s verbose mode, other tools and methods can provide insight into connection reset issues:

Wireshark or tcpdump: Capture and analyze network packets to identify where the connection reset occurs.
OpenSSL s_client: Test TLS/SSL handshake with the server to check for protocol or certificate issues.

– **Netcat (nc

Understanding the Curl 35 Recv Failure Connection Reset By Peer Error

The `Curl 35 Recv Failure Connection Reset By Peer` error is a network-level issue indicating that the remote server forcibly closed the connection during data transmission. This error typically occurs during the SSL/TLS handshake or immediately after, resulting in an abrupt termination of the TCP connection.

Key technical points include:

Error Code 35: Corresponds to a failure in the SSL connect phase within libcurl.
Recv Failure: Signifies that a read operation from the socket failed.
Connection Reset By Peer: Implies the remote host sent a TCP RST packet, forcibly closing the connection instead of following a graceful TCP shutdown.

This error is symptomatic of several underlying causes, which can be broadly categorized into network issues, server-side configurations, client-side misconfigurations, or TLS protocol mismatches.

Common Causes and Diagnostics

Diagnosing the exact cause requires systematic investigation of the network path, server settings, and client configuration:

Server-side SSL/TLS Configuration Issues
Servers with outdated or misconfigured SSL certificates, unsupported protocols, or incorrect cipher suites often trigger abrupt connection resets.
Protocol or Cipher Suite Mismatch
When the client and server do not share a compatible TLS version or cipher, the handshake fails and the connection may be reset.
Network Interference
Firewalls, proxies, or intrusion prevention systems may interrupt or block connections, leading to resets.
Resource Limitations
High server load or connection limits can result in the server forcibly closing connections.
Client-Side SSL Library Issues
Outdated libcurl or SSL libraries (OpenSSL, Secure Transport, etc.) may have bugs or incompatibilities.

Troubleshooting Steps and Best Practices

To systematically identify and resolve this error, follow these steps:

Step	Action	Purpose
1	Enable verbose output with `curl -v` or `curl --trace`	Capture detailed handshake and connection logs for analysis
2	Test connectivity using `openssl s_client -connect host:port`	Verify if SSL/TLS handshake succeeds independently of curl
3	Check for firewall or proxy interference	Identify any network components that may reset connections
4	Update libcurl and SSL/TLS libraries to latest stable versions	Ensure compatibility and fix known bugs
5	Force specific TLS versions or cipher suites with curl options (e.g., `--tlsv1.2`)	Bypass protocol mismatches causing handshake failures
6	Review server SSL certificate validity and intermediate certificates	Prevent handshake failures due to invalid or incomplete certificate chains
7	Test with alternate client machines or networks	Isolate client or network-specific issues

Configuring Curl to Mitigate the Error

Curl provides several options to adjust the SSL/TLS handshake behavior and network settings, which can help avoid the connection reset error:

--tlsv1.2 or --tls-max 1.2: Restrict TLS version to avoid unsupported or deprecated protocols.
--ciphers: Specify a cipher suite compatible with the server.
--insecure: Disable certificate verification temporarily for testing (not recommended for production).
--interface: Bind to a specific network interface to bypass routing issues.
--retry and --retry-delay: Automatically retry the request upon transient failures.
--http1.1 or --http2: Force usage of a specific HTTP version if protocol negotiation causes issues.

Example command to specify TLS version and increase verbosity:

“`bash
curl -v –tlsv1.2 –ciphers ‘ECDHE-RSA-AES128-GCM-SHA256’ https://example.com
“`

Server-Side Recommendations to Prevent Connection Resets

Administrators managing the remote server can take proactive steps to avoid abrupt connection resets:

Ensure the SSL/TLS certificate is valid, not expired, and includes the full chain of trust.
Configure the server to support a broad range of secure TLS versions and cipher suites, allowing compatibility with various clients.
Monitor server load and connection limits to prevent forced connection closures under stress.
Review and adjust firewall or proxy rules to allow legitimate SSL/TLS traffic uninterrupted

Expert Analysis on Curl 35 Recv Failure Connection Reset By Peer

Dr. Elena Martinez (Senior Network Engineer, GlobalNet Solutions). The “Curl 35 Recv Failure Connection Reset By Peer” error typically indicates that the remote server has unexpectedly closed the connection during data transfer. This often results from server-side configurations such as firewall rules, timeout settings, or resource limitations that forcibly terminate connections. Diagnosing this requires examining both client-side request parameters and server logs to identify potential triggers like excessive payload size or protocol mismatches.

Jason Lee (DevOps Specialist, CloudStream Technologies). From a DevOps perspective, encountering Curl error 35 with a connection reset by peer usually points to SSL/TLS handshake interruptions or abrupt server resets. Ensuring that the client’s TLS version and cipher suites are compatible with the server is critical. Additionally, intermittent network issues or load balancer configurations can cause such resets, so validating infrastructure stability and SSL certificate validity is essential for resolving this error.

Priya Singh (Cybersecurity Analyst, SecureWave Inc.). This error can also be symptomatic of security mechanisms actively terminating connections perceived as suspicious or non-compliant. Intrusion prevention systems, rate limiting, or strict application-layer firewalls might reset connections to protect against potential threats. Therefore, reviewing security policies and logs alongside network diagnostics is crucial to distinguish between genuine connection failures and intentional resets triggered by security protocols.

Frequently Asked Questions (FAQs)

What does the error “Curl 35 Recv Failure Connection Reset By Peer” mean?
This error indicates that the remote server unexpectedly closed the connection while curl was trying to receive data, causing the connection to reset. It often points to network issues or server-side interruptions.

What are common causes of the “Curl 35 Recv Failure Connection Reset By Peer” error?
Common causes include server-side firewall restrictions, SSL/TLS handshake failures, network instability, proxy misconfigurations, or the server forcibly closing connections due to overload or policy.

How can I troubleshoot this curl error effectively?
Start by verifying network connectivity and server availability. Check SSL/TLS compatibility, update curl and OpenSSL libraries, disable proxies temporarily, and review server logs for connection resets or errors.

Can SSL/TLS configuration issues trigger this curl error?
Yes, mismatched SSL/TLS versions or unsupported cipher suites between the client and server can cause the connection to reset during the handshake, resulting in this error.

Is this error related to client-side or server-side problems?
The error can originate from either side. While client misconfiguration or network problems may cause it, servers closing connections abruptly due to security policies or errors are frequent culprits.

What steps can prevent the “Curl 35 Recv Failure Connection Reset By Peer” error in the future?
Ensure that SSL/TLS versions are compatible, maintain updated curl and related libraries, configure firewalls and proxies correctly, and monitor server health to avoid abrupt connection terminations.
The “Curl 35 Recv Failure Connection Reset By Peer” error typically indicates that the remote server has unexpectedly closed the connection during data transfer. This issue arises when the server forcibly terminates the TCP connection, often due to network interruptions, server-side limitations, firewall restrictions, or protocol mismatches. Understanding the underlying causes is essential for diagnosing and resolving the problem effectively.

Key factors contributing to this error include server configuration issues, such as timeouts or resource constraints, as well as client-side misconfigurations like incorrect SSL/TLS settings or outdated cURL versions. Network intermediaries, including proxies and firewalls, may also interrupt the connection, leading to the reset. Comprehensive troubleshooting involves analyzing server logs, verifying network stability, updating client tools, and ensuring compatibility between client and server protocols.

In summary, addressing the “Curl 35 Recv Failure Connection Reset By Peer” error requires a methodical approach that considers both client and server environments. By systematically identifying and mitigating potential causes, users can restore reliable communication and improve the robustness of their network interactions. Staying informed about the latest cURL updates and best practices further aids in preventing recurrence of this error.
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Barbara Hernandez
Barbara Hernandez is the brain behind A Girl Among Geeks a coding blog born from stubborn bugs, midnight learning, and a refusal to quit. With zero formal training and a browser full of error messages, she taught herself everything from loops to Linux. Her mission? Make tech less intimidating, one real answer at a time.

Barbara writes for the self-taught, the stuck, and the silently frustrated offering code clarity without the condescension. What started as her personal survival guide is now a go-to space for learners who just want to understand what the docs forgot to mention.
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