An ISAPI DLL registered with Internet Information Services (IIS) that modifies the behaviour of the server. URLScan.dll is an example of a Microsoft®-provided ISAPI filter. Filters are loaded when the worker process starts and unloaded when the worker process shuts down. Also known as filters. to top to top key In the IIS metabase: See node as defined for the IIS metabase. In the Windows registry: A node in the registry. A key can contain subkeys and entries, for example, Environment is a key of HKEY_CURRENT_USER. In IP security (IPSec): A value used in combination with an algorithm to encrypt or decrypt data. Key settings for IPSec are configurable to provide greater security. to top location See node as defined for the IIS metabase.

A DLL that uses the Internet Server API (ISAPI) to register for web server events and edit the data stream going to and coming from the Microsoft IIS web server.

An application, usually a DLL, that sits on the front of IIS and acts as a filter for requests coming into IIS.