HTTP 426 Upgrade Required vs 520 Web Server Returned an Unknown Error
HTTP 426 (Upgrade Required) is a 4xx Client Error response, while 520 (Web Server Returned an Unknown Error) is a 5xx Server Error response. 426 indicates that the server refuses to perform the request using the current protocol but might after the client upgrades to a different protocol. In contrast, 520 means that cloudflare-specific. The origin server returned an unexpected response that Cloudflare could not process.
Description
The server refuses to perform the request using the current protocol but might after the client upgrades to a different protocol.
When You See It
When a server requires HTTPS or a newer protocol version.
How to Fix
Switch to the protocol specified in the Upgrade response header.
Description
Cloudflare-specific. The origin server returned an unexpected response that Cloudflare could not process.
When You See It
When Cloudflare receives an empty, unknown, or malformed response from the origin.
How to Fix
Check origin server logs. Ensure responses include proper headers. Verify SSL configuration.
Key Differences
426 is a 4xx Client Error response, while 520 is a 5xx Server Error response.
HTTP 426: The server refuses to perform the request using the current protocol but might after the client upgrades to a different protocol.
HTTP 520: Cloudflare-specific. The origin server returned an unexpected response that Cloudflare could not process.
You encounter 426 when when a server requires HTTPS or a newer protocol version.
You encounter 520 when when Cloudflare receives an empty, unknown, or malformed response from the origin.
When to Use Which
For 426 (Upgrade Required): Switch to the protocol specified in the Upgrade response header. For 520 (Web Server Returned an Unknown Error): Check origin server logs. Ensure responses include proper headers. Verify SSL configuration.