Introduction

Your Web server thinks that the HTTP data stream sent by the client (e.g. your Web browser or our CheckUpDown robot) contains a 'Range' request which specifies a range of bytes which can not be satisfied - because the resource being accessed does not cover this byte range. For example if the resource - an image file for example - has 1000 bytes and the Range requested is 500-1500, then it can not be satisfied.

416 errors in the HTTP cycle

Any client (e.g. your Web browser or our CheckUpDown robot) goes through the following cycle:

• 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. We 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 '416'.

Resolving 416 errors - general

This error seldom occurs in most Web traffic, particularly when the client system is a Web browser. The URLs in this case are typically standard hyperlinks found on Web pages, which very seldom use the 'Range' specification.

If your client system is not a Web browser, the problem can only be resolved by examining what the client is trying to do then discussing with your ISP why the Web server rejects the 'Range' specification sent by the client system. Most often this is due to a badly written client system which uses the 'Range' specification but disregards the total size of the resource being requested.

Resolving 416 errors - CheckUpDown

This error should simply never occur on 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 the Range request at all, because we always want the entire content of the URL you ask us to monitor.

Please contact us (email preferred) whenever you encounter 416 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.