When using residential proxies to access websites or online services, encountering errors can disrupt your workflow. One such error is Error 521, which occurs when the origin server (the website’s hosting server) refuses the connection initiated by Cloudflare, a widely used content delivery network (CDN) and security service. Error 521 is a web server down error that occurs when Cloudflare attempts to connect to the origin server, but the server refused the connection. This typically happens when the origin server is offline, misconfigured, or experiencing technical issues.
The error message usually reads:
“Error 521: Web server is down.”
Why Does Error 521 Occur?
- Server Offline: The origin server may be completely down due to maintenance, hardware failure, or power outages.
- Firewall Restrictions: The server’s firewall may be blocking Cloudflare’s IP addresses, preventing a connection.
- Misconfigured Server: Incorrect server settings, such as port configurations or SSL/TLS issues, can cause the server to refuse connections.
- Network Issues: Connectivity problems between Cloudflare and the origin server, such as routing issues or ISP outages, can lead to this error.
- Proxy Misconfiguration: If you’re using a proxy, incorrect settings or low-quality proxies can contribute to connection issues.
How to Fix Error 521
1. Check the Origin Server
Verify if the origin server is online and functioning properly. Use tools like Ping or Traceroute to test the server’s availability.
Contact the website owner or hosting provider to confirm if there are any server-side issues.
2. Review Firewall Settings
Ensure that the server’s firewall is not blocking Cloudflare’s IP addresses.
Whitelist Cloudflare’s IP ranges to allow seamless communication. You can find Cloudflare’s IP list on their official website.
3. Check Server Configuration
Verify that the server is configured correctly, including port settings and SSL/TLS certificates.
Ensure that the server is listening on the correct port (e.g., port 80 for HTTP or port 443 for HTTPS).
4. Test Network Connectivity
Check the network connection between Cloudflare and the origin server to identify any connectivity issues.
If you’re using a proxy, try switching to a different proxy server or location to see if the issue persists.
5. Restart the Server
If the server is experiencing temporary issues, restarting it may resolve the problem.
Ensure that all necessary services (e.g., web server, database) are running after the restart.
6. Use a Different Proxy
If the issue persists, switch to a different proxy server or provider. High-quality proxies, such as those offered by NodeMaven, are less likely to cause connection issues. US proxy of NodeMaven are very popular on the market.
Preventing Error in the Future
- Use reliable, high-performance proxies from trusted providers like NodeMaven.
- Regularly monitor the health and performance of your origin server.
- Ensure proper configuration of both your proxy settings and the origin server.
- Implement redundancy by using multiple proxy servers or locations to minimize downtime.
Error 521 is a connection refusal issue that can occur when using proxies, but it can be resolved by identifying and addressing its root causes. By checking the origin server, reviewing firewall settings, and ensuring proper proxy configuration, you can minimize the risk of encountering this error.
For reliable and high-performance proxies that reduce the likelihood of errors like 521, consider NodeMaven and its mobile proxies. Their robust infrastructure and global IP pool ensure seamless connectivity and an enhanced online experience.