Recently one of my friend has some trouble in IIS hosted application. To identify the RCA I got to know the advance feature of IIS 6.. Enclosed the extract of that knowledge..
Windows Server 2003 introduced some significant changes from Windows 2000 Server, and Internet Information Services (IIS) 6.0 is a good example. Not only is IIS' architecture considerably different in IIS 6.0, but the management interface has also changed. For example, IIS 6.0 provides two operating modes: IIS 5.0 Isolation Mode and IIS 6.0 Worker Process Isolation Mode.
In IIS 5.0 Isolation Mode, all in-process applications run inside Inetinfo.exe. Out-of-process applications run in separate instances of DLLHost.exe. Inetinfo.exe handles HTTP request queuing, IIS services (FTP, SMTP, NNTP, etc.), and worker processes. Svchost.exe runs the WWW service.
The primary purpose for IIS 5.0 Isolation Mode is to mimic the behavior of IIS 5.0 and earlier versions, and it provides compatibility for Web applications designed specifically for IIS 5.0 or earlier.
IIS 6.0 Worker Process Isolation Mode, also called native mode, provides better performance, reliability, and fault tolerance. In native mode, the kernel-mode driver http.sys handles all HTTP request processing and queuing. Inetinfo.exe handles IIS administration and configuration as well as the IIS services, including SMTP, NNTP, and FTP. Svchost.exe handles the WWW service, and multiple instances of W3wp.exe handle worker processes.
Separating worker processes in this way isolates those worker processes from the core IIS services for better reliability overall and better recoverability for individual processes. This process isolation, combined with the fact that the core IIS services prevent the loading of third-party code, means an errant Web application will have a tough time crashing the WWW service and bringing down the server.
In a clean installation of IIS 6.0, native mode is the default mode. A system upgraded from a previous IIS 6.0 installation assumes the mode of the previous installation. Systems upgraded from IIS 5.0 or IIS 4.0 run in IIS 5.0 Isolation Mode to provide compatibility for the existing Web applications on the server.
One aspect of managing an IIS 6.0 server is setting the mode in which the server runs. For example, you might be installing a Web application that won't run in native mode and need to switch the server to IIS 5.0 Isolation Mode. Or you may have upgraded an existing server and now want to switch it from IIS 5.0 Isolation Mode to native mode. Note that the server as a whole runs in a given mode; you can't run specific sites on the server in different modes.
To configure IIS 6.0's operation mode, open the Internet Information Services Manager from the Administrative Tools folder, or run %systemroot%\system32\inetsrv\iis.msc. When the IIS console opens, right-click the Web Sites branch in the left pane, choose Properties, and select the Service tab. Selecting the Run WWW Service In IIS 5.0 Isolation Mode option configures the server to run in IIS 5.0 Isolation Mode. Deselect this option if you want to run the server in native mode.