HTTP 416 Range Not Satisfiable vs 521 Web Server Is Down
HTTP 416 (Range Not Satisfiable) is a 4xx Client Error response, while 521 (Web Server Is Down) is a 5xx Server Error response. 416 indicates that the server cannot serve the requested byte range. The Range header value is outside the resource's size. In contrast, 521 means that cloudflare-specific. The origin server refused the connection.
Description
The server cannot serve the requested byte range. The Range header value is outside the resource's size.
When You See It
When requesting a byte range beyond the file's actual size.
How to Fix
Check the Content-Range in the response for the actual file size and adjust your Range header.
Description
Cloudflare-specific. The origin server refused the connection.
When You See It
When Cloudflare can't establish a TCP connection to the origin server.
How to Fix
Check that the origin server is running and the firewall allows Cloudflare IPs.
Key Differences
416 is a 4xx Client Error response, while 521 is a 5xx Server Error response.
HTTP 416: The server cannot serve the requested byte range. The Range header value is outside the resource's size.
HTTP 521: Cloudflare-specific. The origin server refused the connection.
You encounter 416 when when requesting a byte range beyond the file's actual size.
You encounter 521 when when Cloudflare can't establish a TCP connection to the origin server.
When to Use Which
For 416 (Range Not Satisfiable): Check the Content-Range in the response for the actual file size and adjust your Range header. For 521 (Web Server Is Down): Check that the origin server is running and the firewall allows Cloudflare IPs.