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HTTP Error 406 - Not acceptable
Introduction
A client (e.g. your Web browser or our CheckUpDown robot) can
indicate to the Web server characteristics of the data it will accept back
from the Web server. This is done using 'accept headers' of the following
types:
a.. Accept: The MIME types accepted by the client. For example, a
browser may only accept back types of data (HTML files, GIF files etc.) it
knows how to process.
b.. Accept-Charset: The character sets accepted by the client.
c.. Accept-Encoding: The data encoding accepted by the client e.g.
the file formats it understands.
d.. Accept-Language: The natural languages (English, German etc.)
accepted by the client.
e.. Accept-Ranges: Whether the client accepts ranges of bytes from
the resource i.e. a portion of the resource.
If the Web server detects that the data it wants to return is not
acceptable to the client, it returns a header containing the 406 error code.
406 errors in the HTTP cycle
Any client (e.g. your Web browser or our CheckUpDown robot) goes
through the following cycle:
a.. 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).
b.. Open an IP socket connection to that IP address.
c.. Write an HTTP data stream through that socket.
d.. 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 '406'.
Resolving 406 errors - general
This error occurs very infrequently in Web browsers, because most
browsers will accept any data returned from your Web server.
If the client is not a Web browser, then anyone can only investigate
the problem by looking at the Accept headers generated by the client system
and the data stream returned by the Web server. If you do not have access to
the source code for these systems, the only thing you can do is refer the
problem to technical support people at the companies that developed the
systems.
Resolving 406 errors - CheckUpDown
This error should simply never occur in your CheckUpDown account. If
it does, it typically indicates defective programming of our systems or of
the Web server which manages your site. We do not use accept headers at all,
so there is no reason for your Web server to generate a 406 error.
Please contact us (email preferred) whenever you encounter 406
errors - there is nothing you can do to sort them out. We then have to
liaise with your ISP and the vendor of your Web server software to agree the
exact reason for the error.
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