HTTP 404 ERROR
The HTTP 404, 404 Not Found, 404, Page Not Found, or Server Not Found error message is a Hypertext Transfer Protocol (HTTP) standard response code, in computer network communications, to indicate that the browser was able to communicate with a given server, but the server could not find what was requested. Further, when the requested information is found but access is not granted, the server may return a 404 error if it wishes to not disclose this information, as well.
The website hosting server will typically generate a “404 Not Found” web page when a user attempts to follow a broken or dead link; hence the 404 error is one of the most recognizable errors encountered on the World Wide Web.
Microsoft Internet Server 404 substatus error codes
The webserver software developed by Microsoft, Microsoft’s Internet Information Services (IIS), returns a set of substatus codes with its 404 responses. The substatus codes take the form of decimal numbers appended to the 404 status code. The substatus codes are not officially recognized by IANA and are not returned by non-Microsoft servers.
Substatus codes
Microsoft’s IIS 7.0, IIS 7.5, and IIS 8.0 servers define the following HTTP substatus codes to indicate a more specific cause of a 404 error:
- 404.0 – Not found.
- 404.1 – Site Not Found.
- 404.2 – ISAPI or CGI restriction.
- 404.3 – MIME type restriction.
- 404.4 – No handler configured.
- 404.5 – Denied by request filtering configuration.
- 404.6 – Verb denied.
- 404.7 – File extension denied.
- 404.8 – Hidden namespace.
- 404.9 – File attribute hidden.
- 404.10 – Request header too long.
- 404.11 – Request contains double escape sequence.
- 404.12 – Request contains high-bit characters.
- 404.13 – Content length too large.
- 404.14 – Request URL too long.
- 404.15 – Query string too long.
- 404.16 – DAV request sent to the static file handler.
- 404.17 – Dynamic content mapped to the static file handler via a wildcard MIME mapping.
- 404.18 – Query string sequence denied.
- 404.19 – Denied by filtering rule.
- 404.20 – Too Many URL Segments.
Tracking 404 errors
A number of tools exist that crawl through a website to find pages that return 404 status codes. These tools can be helpful in finding links that exist within a particular website. The limitation of these tools is that they only find links within one particular website, and ignore 404s resulting from links on other websites. As a result, these tools miss out on 83% of the 404s on websites. One way around this is to find 404 errors by analyzing external links.
Another common method is tracking traffic to 404 pages using log file analysis. This can be useful to understand more about what 404s users reached on the site. Another method of tracking traffic to 404 pages is using JavaScript-based traffic tracking tools.
