The HyperText Transfer Protocol (HTTP) error 505 : HTTP Version Not Supported response status code indicates that the HTTP version used in the request is not supported by the server.

As a part of our Server Management Services, we help our Customers to fix HTTP related errors regularly.

Let us today discuss the possible causes and fixes for this error.

What is HTTP error 505 : HTTP version not supported?

Whenever a client communicates with a web server, it follows a series of steps. For instance, a brief listing of it includes:

1. Obtain an IP address from the IP name of the site (the site URL without the leading ‘http://’). This lookup (conversion of IP name to IP address) is provided by domain name servers (DNSs).
2. Open an IP socket connection to that IP address.
3. Write an HTTP data stream through that socket.
4. Receive an HTTP data stream back from the Web server in response. This data stream contains status codes whose values are determined by the HTTP protocol. Parse this data stream for status codes and other useful information.

When the webserver does not support or refuses to support the HTTP protocol version specified by the client in the HTTP request data stream sent to the server, then it returns the 505 error final stage above. A typical error message looks like the one below:

The possible reasons for this error include:

1. The server is indicating that it is unable or unwilling to complete the request using the same major version of HTTP protocol as the client.
2. If there is whitespace after the HTTP version
3. Bad URL copied in the telnet connection
4. If the client is not a web browser

How to fix HTTP error 505 : HTTP version not supported?

The HTTP protocol has various versions identified as major or minor. Mostly, with this error, the server is indicating that it is unable or unwilling to complete the request using the same major version as the client. The server will generate a representation for the 505 response that describes why that version is not supported and what other protocols are supported by that server.

To test this, open a telnet connection to a couple of major websites, and execute the following command:

GET / HTTP/4.0

You may receive a response as shown below:

HTTP/1.1 505 HTTP Version Not Supported
Server: cloudflare
Date: Tue, 17 Aug 2020 15:23:35 GMT
Content-Type: text/html
Content-Length: 201
Connection: close

If you see this error in your Web browser, try a newer version or switch to a modern browser to see if the error goes away. Further, if you still see this error in your Web browser, upgrade your orgin Web server software to support the major version of the http protocol you require.

The error message should indicate what protocols are supported by your origin server. Thus we need to review those protocols to troubleshoot the error. The error may specifically indicate what program name does not support the protocol. If so, review that information to troubleshoot the error.

Also, make sure that there is no whitespace after the HTTP version as it can also trigger this error. It is also important to make sure that the URL is correct and contains no special characters

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Conclusion

In short, HTTP error 505 indicates that the HTTP version used in the request is not supported by the server. Today, we saw how our Support Engineers fix this error.