HTTP/1.1 Error 501 - Not Implemented

This article discusses a by-design HTTP error 501 that occurs when you use an unknown method from an Internet client.

Original product version:   Internet Information Services (IIS)
Original KB number:   247643

Symptoms

When you attempt to use an unknown method from an Internet client, the following error message occurs:

HTTP/1.1 501 Not Implemented

Cause

This behavior is by design. Microsoft Internet Information Services (IIS) only supports the methods defined in RFC 2616 - Hypertext Transfer Protocol--HTTP/1.1 and RFC 2518 - HTTP Extensions for Distributed Authoring--WEBDAV. The methods are listed in the following table: