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Introduction
Your Web server 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. Your 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 your
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 your Web server:
- Obtain an IP address from the IP name of your site (your 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 your 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'.
Resolving 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 your Web server software. If version 1.x requests
fail, it may well be because your 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.
Resolving 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 your Web site. If these fail, it may well be because your 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 your 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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