523
Unofficial (Cloudflare)
523 Origin Is Unreachable: Network‑Level Connectivity Failure
✦ The Golden Answer: The 523 Origin Is Unreachable is a Cloudflare-specific status code. It indicates that Cloudflare could not reach the origin server due to network-level issues. Unlike 521 (which means the web server refused the connection) or 522 (which is a timeout), 523 means the origin server is completely unreachable from the network layer — there is no route to the host, the server is powered off, or the IP address is unreachable. This is usually a more severe issue, often caused by network outages, misconfigured DNS, or the server being offline.
Common Causes of 523 Errors
| Cause | Example | How to Fix |
|---|---|---|
| Server is offline or powered off | Physical server shutdown or cloud instance stopped. | Start the server or cloud instance; check power or cloud console. |
| Network routing issue | ISP or network provider has a routing problem. | Contact your hosting provider or ISP; check network connectivity from your server. |
| DNS resolution failure | Cloudflare cannot resolve the origin server's hostname to an IP. | Verify DNS records (A/AAAA) are correct and propagated. Use a reliable DNS provider. |
| Firewall blocking all traffic | Firewall rules block all incoming connections from Cloudflare's IPs. | Whitelist Cloudflare IP ranges in your firewall. |
| IP address changed | Origin server's IP address changed, but DNS still points to the old IP. | Update DNS records with the new IP and wait for propagation. |
Example: Cloudflare 523 Error Page
Cloudflare displays a user‑friendly error page for 523 errors:
HTTP/1.1 523 Origin Is Unreachable
Content-Type: text/html
<html>
<body>
<h1>523: Origin Is Unreachable</h1>
<p>The origin server is not reachable. Please check your network connectivity.</p>
</body>
</html>
How to Fix 523 Errors
- Check server status: Ensure your server is powered on and has a working network interface. If you're using a cloud provider, check the instance status in the console.
- Verify DNS records: Ensure your domain's A/AAAA records point to the correct IP address. Use
digornslookupto check DNS resolution from outside your network. - Test network connectivity: From a separate location, try to ping or traceroute to your server's IP. If it fails, the issue is likely with your hosting provider or ISP.
- Check firewall rules: Ensure your firewall allows inbound connections on ports 80 and 443 from Cloudflare's IP ranges. You can find Cloudflare's IP list at
https://www.cloudflare.com/ips/. - Contact your hosting provider: If you cannot resolve the issue, contact your hosting provider or network administrator.
Preventing 523 Errors
- Use a monitoring service: Set up uptime monitoring to alert you when your server becomes unreachable.
- Implement redundancy: Use multiple origin servers or a load balancer to reduce single points of failure.
- Keep DNS records up to date: Use a dynamic DNS service or automate DNS updates if your IP changes frequently.
- Regularly review firewall rules: Ensure Cloudflare IP ranges are kept up to date.
Frequently Asked Questions
Is 523 a client error or a server error?
It is a server error (5xx) because the origin server is completely unreachable. Cloudflare is working correctly but cannot establish any network connection to the origin.
Can I fix a 523 error from the client side?
No, it is a server‑side network issue. Only the website owner or server administrator can fix it.
What is the difference between 523 and 521?
521 means the web server process (e.g., Nginx) is not running or refuses connections. 523 means the server is completely unreachable at the network level (e.g., no route to host, server offline).