Relationship between Error 521 and DNS Setting Error and Troubleshooting Methods

Did your website suddenly appear Error 521 The page does not open, there is only one line: "Web server is down". The page won't open, there is only one line: "Web server is down". And you check theserver (computer)When you realize that the server is actually not hanging at all, it's time to consider an often-overlooked problem - theIncorrect DNS settingsThe

A lot of people think that the 521 error is justserver (computer)There is often a close connection between DNS settings and the lack of response. This article will take you through the relationship between them, and teach you how to troubleshoot and fix it.

What problems can incorrect DNS settings cause?

DNS is like a "navigational sign" for a website, telling visitors (including Cloudflare) where your server is located. If this address is wrong, the request will not reach the real server.

in use Cloudflare When the DNS setting is wrong, it is a direct result:

• Requests are forwarded to the wrong IP, not your server at all!
• Cloudflare cannot connect to the source station, displaying 521
• You obviously have the server running fine, but the page is still not accessible

Many people reboot their servers, check their firewalls, and ignore the DNS configuration.

What are some common DNS setting errors?

1. A record is set to the wrong IP address

This is the most typical error, for example if you moved servers but didn't update the A record in DNS, Cloudflare is still trying to access the old server address and of course the connection fails.

method settle an issue: Go to the DNS control panel and make sure that the IP pointed to by the A record is the public IP of your current server.

2. A record does not have "proxy status" enabled

Cloudflare's DNS There is an "Orange Cloud" icon that indicates whether the proxy service is enabled or not. If you're using a CDN and don't have this option enabled, it may cause errors in the connection between Cloudflare and the server.

Recommended settings: Set the domain name that needs to use CDN to "Proxy Status On" to display the orange cloud icon.

3. Incorrectly configured subdomain records or duplicate records

Sometimes you may have inadvertently added multiple records pointing to the same subdomain, or the subdomain may be spelled incorrectly.Cloudflare may have selected the wrong record when parsing.

Inspection Methods: Cleans up invalid or duplicate DNS records and retains the correct A record or CNAME.

4. Unnecessary AAAA records set (IPv6)

If the server is not configured for IPv6, but you have added AAAA records, this can also cause Cloudflare to fail in its attempts to connect over IPv6.

Recommendation processing: Delete useless AAAA records and keep only the IP types you do use.

How can I confirm if the 521 is caused by a DNS issue?

You can start with these:

• In the Cloudflare backend → DNS → see if the current A record is correct
• Directly ping the domain name locally to see if the resolved IP is that of your real server.
• Use tools such as https://dnschecker.org/ View Global Resolutions
• View in server Nginx or Apache's access logs for requests originating from Cloudflare's IPs

If there are no access logs, it means that the request did not reach the server at all, and the probability is that it is a DNS or network path problem.

Summary of troubleshooting recommendations

1. Verify that the A record in DNS is filled with the correct server IP.
2. Check if Cloudflare agent is enabled (orange cloud status)
3. Delete useless AAAA or error subdomain records
4. Test again after clearing the local and Cloudflare DNS caches
5. If that doesn't work, try switching the domain to "DNS-only" mode to bypass the CDN and test the source connection.

reach a verdict

Error 521 is not necessarily server down, and not alwaysfirewallsThe problem. Often it's just that Cloudflare can't find your server at all because the DNS configuration isn't done properly. Setting up A records correctly and checking your DNS panel regularly are the basics of keeping your website running stably.

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