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HTTP Error 505 - HTTP version
not supported
Introduction
The Web server (running the Web site) does not support, or
refuses to support, the HTTP protocol version specified by the client (e.g.
your Web browser or our CheckUpDown robot) in the HTTP request data stream sent
to the server.
The HTTP protocol has various versions identified as
major.minor e.g. version 0.9, 1.0 or 1.1. The server is indicating that
it is unable or unwilling to complete the request using the major version
provided by the client - other than with this error message.
Assuming that your request identifies a valid major.minor
version number (the request is not fundamentally corrupt), then this error
should mostly only occur if you are trying to use version 1.0 or 1.1, but the
Web server only supports the older 0.9 version.
505 errors in the HTTP cycle
Any client (e.g. your Web browser or our CheckUpDown robot) goes
through the following cycle when it communicates with the Web server:
- 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).
- Open an IP socket connection to that IP address.
- Write an HTTP data stream through that socket.
- 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.
This error occurs in the final step above when the client
receives an HTTP status code that it recognises as '505'.
Fixing 505 errors - general
Most Web browsers assume that Web servers support 1.x versions
of the HTTP protocol. In practice very old versions such as 0.9 are little used
nowadays, not least because they provide poorer security and performance than
newer versions of the protocol. So if you see this error in your Web browser,
the only option is to upgrade the Web server software. If version 1.x requests
fail, it may well be because the Web server is supporting the 1.x protocol
versions badly, rather than not supporting them at all.
The same arguments apply if your client is not a Web
browser.
Fixing 505 errors - CheckUpDown
It is our responsibility to support whatever versions of the
HTTP protocol all Web servers understand. Because very old versions such as 0.9
are little used nowadays, our CheckUpDown robot uses 1.x versions of HTTP when
we try to access the Web site. If these fail, it may well be because the Web
server is supporting the 1.x protocol versions badly, rather than not
supporting them at all.
Please contact us (email preferred) whenever you encounter 505
errors - there is nothing you can do to sort them out. We then have to analyse
the underlying HTTP data streams and may have to liaise with your ISP and the
vendor of the Web server software to agree how different HTTP protocol versions
should be supported. In the worst case we may have to revise our program code
supporting particular HTTP versions, which may take some time.
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