HTTP Error 406 - Not acceptable
Posted by admin on August 24 2008 23:33:31

406 errors in the HTTP

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:

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:

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.

The resource identified by the request is only capable of generating response entities which have content characteristics not acceptable according to the accept headers sent in the request.

Unless it was a HEAD request, the response SHOULD include an entity containing a list of available entity characteristics and location(s) from which the user or user agent can choose the one most appropriate. The entity format is specified by the media type given in the Content-Type header field. Depending upon the format and the capabilities of the user agent, selection of the most appropriate choice MAY be performed automatically. However, this specification does not define any standard for such automatic selection.

      Note: HTTP/1.1 servers are allowed to return responses which are 
not acceptable according to the accept headers sent in the request.
In some cases, this may even be preferable to sending a 406 response.
User agents are encouraged to inspect the headers of an incoming response
to determine if it is acceptable.

If the response could be unacceptable, a user agent SHOULD temporarily stop receipt of more data and query the user for a decision on further actions.