What is Erreur 521? How to solve it quickly

This article analyzes the causes of Erreur 521 and its association with proxy IP services, provides general solutions, and explores how to avoid such errors by optimizing proxy selection.

What is Erreur 521?

Erreur 521 is the HTTP status code returned by the Cloudflare platform, indicating that the connection between the target server and Cloudflare has been interrupted. When the website visited by the user uses Cloudflare as a CDN service, this error is triggered if the source server is unresponsive. For enterprises or individuals who rely on proxy IPs for data collection, advertising verification, and other operations, Erreur 521 may directly lead to task interruption. For example, when using a proxy IP to access a website protected by Cloudflare, if the proxy server fails to communicate with the source station, the user will see the prompt "Error 521: Web server is down".

As a brand that provides a variety of proxy IP services, abcproxy users may encounter such problems in certain scenarios. This article will analyze from the perspectives of technical principles, solutions and proxy service optimization.

Why did Erreur 521 appear?

The core reason for Erreur 521 is that Cloudflare cannot establish a valid connection with the origin server. Its triggering conditions include:

The origin server is down or overloaded: The server cannot respond to requests due to hardware failure, traffic surge, or configuration error.

Firewall or security policy interception: The server firewall may mistakenly identify Cloudflare's IP as a threat source and actively cut off the connection.

The proxy IP is marked as abnormal traffic: When high-frequency access is initiated through the proxy IP, Cloudflare may reject the connection due to detecting unusual behavior.

It is worth noting that the use of proxy IP scenarios (such as batch crawling data) can easily trigger security protection mechanisms. If the proxy IP is of poor quality, such as the IP address being reused by a large number of users, the probability of triggering Erreur 521 will be further increased.

How to quickly solve Erreur 521?

Universal solution

Check the target server status: Use third-party tools (such as DownDetector) to confirm whether the website is down globally.

Adjust request frequency : Reduce access frequency to simulate human operation intervals and avoid triggering rate limits.

Change IP or switch protocol : Try using a different IP address or switch from HTTP to HTTPS protocol.

Proxy service optimization suggestions

If the problem is caused by the proxy IP, first ensure that the proxy pool has the following features:

High anonymity: Use residential proxies or static ISP proxies to avoid using shared IPs from public data centers.

IP rotation capability: supports automatic switching of IP addresses to reduce the request density of a single IP.

Protocol compatibility: supports protocols such as SOCKS5, bypassing some network layer restrictions.

For example, abcproxy's static ISP proxy provides exclusive IP and fixed session persistence functions, which can effectively reduce the risk of connection interruption caused by frequent IP changes.

How is Erreur 521 related to proxy IP services?

Proxy IP is a core tool to bypass geographical restrictions or achieve high-frequency access, but its use itself may increase the probability of Erreur 521:

IP reputation issues: Low-quality proxy IPs may have been blacklisted by Cloudflare.

Connection stability: If the data center proxy server is overloaded, the handshake with Cloudflare may fail.

Protocol configuration: Some proxy services do not correctly configure the SSL/TLS protocol, causing compatibility issues.

Therefore, it is very important to choose a proxy service provider with mature technology. Taking abcproxy as an example, its unlimited residential proxy product can significantly reduce errors triggered by abnormal traffic characteristics by simulating real user behavior and dynamically allocating IP pools.

How to choose the right proxy IP to avoid Erreur 521?

Key indicator screening

IP type: Residential proxy or static ISP proxy is preferred, as this type of IP is closer to the real user environment.

Success rate and latency: Require service providers to provide real-time statistics to ensure that the connection success rate is higher than 99%.

Session control: Support long session maintenance (such as 24-hour fixed IP) to avoid frequent re-establishment of connections.

Technical adaptation suggestions

Add retry mechanisms and timeout settings at the code level, such as configuring the max_retries parameter in the Python request library.

Combined with User-proxy rotation and request header randomization, it further conceals automated behavior characteristics.

abcproxy's data center proxy supports API dynamic extraction of IP. Users can flexibly adjust resource configuration according to task requirements to achieve a balance between performance and stability.

Summarize

The solution to Erreur 521 requires both technical troubleshooting and the reliability of the underlying proxy service. Whether it is caused by source server failure or improper proxy IP configuration, optimizing the tool chain and infrastructure is the core response strategy.

As a professional proxy IP service provider, abcproxy provides a variety of high-quality proxy IP products, including residential proxy, data center proxy, static ISP proxy, Socks5 proxy, unlimited residential proxy, suitable for web acquisition, e-commerce, market research, social media marketing, website testing, public opinion monitoring, advertising verification, brand protection, travel information aggregation and other application scenarios. If you are looking for a reliable proxy IP service, welcome to visit the abcproxy official website for more details.