505 HTTP Version Not Supported
505 HTTP Version Not Supported is a status that a server can emit if
it doesn’t support the major HTTP version the client used to make the request.
To test this, I opened a telnet connection to a couple of major websites, and wrote the following:
GET / HTTP/4.0
A few sites returned a
400 Bad Request, but at least Cloudflair returned
HTTP/1.1 505 HTTP Version Not Supported Server: cloudflare Date: Tue, 30 Jul 2019 15:23:35 GMT Content-Type: text/html Content-Length: 201 Connection: close CF-RAY: - <html> <head><title>505 HTTP Version Not Supported</title></head> <body bgcolor="white"> <center><h1>505 HTTP Version Not Supported</h1></center> <hr><center>cloudflare</center> </body> </html>
Currently you’re unlikely to run into this error though, unless you have a buggy client.
We did get a new major HTTP version (2) and a new one is on the way (3), but the mechanism for switching to HTTP/2 or 3 is different, and will just be ignored if a HTTP/1.1 server didn’t support the new version.
- RFC7231, Section 6.6.6 - 505 HTTP Version Not Supported