Internet Information Server (IIS)

A software program for hosting and managing Web applications on Microsoft Windows platform.।
Internet Information Server (IIS) is a World Wide Web server, a Gopher server and an FTP server all rolled into one. IIS means that you can publish WWW pages and extend into the realm of ASP (Active Server Pages) whereby JAVA or VBscript (server side scripts) can generate the pages on the fly. IIS has fun things like application development environment (FrontPage), integrated full-text searching (Index Server), multimedia streaming (NetShow), and site management extensions.
Internet Information Services (IIS) 6.0
Internet Information Services (IIS) 6.0 provide the services to support a secure, available, and scalable Web server on which to run your Web sites and applications.
IIS 6।0 Request Processing ModelsWorker process isolation mode is the new IIS request processing model. In this application isolation mode, you can group Web applications into application pools, through which you can apply configuration settings to the worker processes that service those applications.




Architecture of Worker Process Isolation Mode by IIS 6.0

Application Pool
· W3wp.exe
· Worker Process
· ISAPI Extensions
· ISAPI Filters

Lsass.exe
Inetinfo.exe
Svchost.exe

Application Pool
An Application Pool can contain one or more applications and allows us to configure a level of isolation between different Web applications.

Example: if you want to isolate all the Web applications running in the same computer, you can do this by creating a separate application pool for every Web application and placing them in their corresponding application pool. Because each application pool runs in its own worker process, errors in one application pool will not affect the applications running in other application pools.

W3wp.exe
w3wp.exe is a process associated with application pool in ISS. If you have more than one application pool, you will have more than one instance of w3wp.exe running. This process usually allocates large amounts of resources. This program is important for the stable and secure running of your computer and should not be terminated.

Worker Processes
A worker process is user-mode code whose role is to process requests, such as processing requests to return a static page, invoking an ISAPI extension or filter, or running a Common Gateway Interface (CGI) handler.

In both application isolation modes, the worker process is controlled by the WWW service. However, in worker process isolation mode, a worker process runs as an executable file named W3wp.exe,

Worker processes use HTTP.sys to receive requests and to send responses by using HTTP. Worker processes also run application code, such as ASP.NET applications and XML Web services. You can configure IIS to run multiple worker processes that serve different application pools concurrently.

ISAPI consists of two components: Extensions and Filters. These are the only two types of application that can be developed using ISAPI. Both Filters and Extensions must be written in C++ and compiled into DLL files which are then registered with IIS to be run on the web server.

Lsass.exe
"lsass.exe" is the Local Security Authentication Server. It verifies the validity of user logons to your PC/Server. It generates the process responsible for authenticating users for the Winlogon service. This process is performed by using authentication packages such as the default Msgina.dll. If authentication is successful, Lsass generates the user's access token, which is used to launch the initial shell. Other processes that the user initiates inherit this token.

Inetinfo.exe
"inetinfo.exe" belongs to Microsoft Internet Information Services (IIS) and is used for debugging.

svchost.exe
svchost.exe is a system process belonging to the Microsoft Windows Operating System which handles processes executed from DLLs.