The document provides an overview of the key components of Internet Information Services (IIS). IIS fulfills the role of a web server by responding to requests for files and logging activity. It maintains information about content locations, security access, and URL mappings. The core components of IIS include HTTP.sys, the WWW service, worker processes (W3wp.exe), ISAPI extensions and filters, and application pools. HTTP.sys receives requests and passes them to worker processes. The WWW service manages the configuration and application pools. Worker processes execute application code and use ISAPI components to process requests and return responses.

1. “Understanding our IIS - Part1”

2. Remember This?

3. Web Server
• The primary function of a web server is to
deliver web pages on requests from clients using
HTTP.
• It can be referred as hardware(computer) or the
software (computer application)
• Hosts websites/web application to serve www.
• Found embedded in devices like printers,
routers, web-cams to serve local network
• Able to map URL to a local file system resource
(static requests) as well as internal or external
program name (dynamic requests)

4. IIS
• IIS fulfills the role of Web Server, responding to
request for files and logging activity.
• IIS maintain the info about
– The location of the content files
– What security identities have access
– How content files are separated in apps
– Provides what URLs are mapped to those
apps
• IIS Administrative Tools helps you to make web
content creation fast and easy

5. IIS Components
• Kernel Mode
– HTTP.sys
• User Mode
– WWW Service
– Worker processes (W3wp.exe)
– ISAPI
– ISAPI Components (Extensions & Filters)
– Application Pools

6. Remember This Again?

7. HTTP.sys
• Also known as “HTTP Protocol Stack” or “Http
Listener Process”
• Implemented as a kernel-mode device driver
• Core component to receive and serve HTTP
requests and passing them off to the worker
processes
• When you create a Web site, IIS registers the site
with HTTP.sys
• Other than retrieving a stored response from its
internal cache, HTTP.sys does not process the
requests that it receives.

8. WWW Service
• Also known as “W3Svc”or“Svchost.exe”
• It manages the IIS metabase
(Metabase.bin) + monitors W3p.exe
• Metabase is a config file for IIS (like a
registry) available for other apps
• Manages application pools and starting,
stopping and recycling w3c process
• WWW Service also collect the counters
for Web sites

9. W3wp.exe
• A worker process is user-mode code whose role is
to process requests, such as processing requests
to return a static page
• A worker process runs as an executable file
named W3wp.exe
• Worker processes also run application code, such
as ASP.NET applications and XML Web services.
• Multiple W3wp.exe can run for a single website
• Each worker process internally use ISAPI
Extensions and Filters

10. ISAPI
• Internet Server Application Programming
Interface, is an API developed to provide the
application developers with a powerful way to
extend the functionality of IIS
• Extensions and Filters are the two types of
applications that can be developed using ISAPI
• ISAPI extensions are true applications that run on
IIS and have access to all of the functionality
provided by IIS while filters are local to IIS used
to put checkpoints for incoming/outgoing data

11. ISAPI Extensions
• ISAPI extensions are implemented as DLLs that
are loaded into a process that is controlled by IIS
• Like ASP and HTML pages, IIS uses the virtual
location of the DLL file in the file system to map
the ISAPI extension
• ASP.Net functionality is contained in an ISAPI
extension called aspnet_isapi.dll
• Any file that is requested from the IIS server that
ends in “.aspx” is mapped to aspnet_isapi.dll
which is assigned to process the file before
displaying its output in the client’s window

12. ISAPI Filters
• ISAPI filters are DLL files that can be used to
modify and enhance the functionality provided
by IIS
• ISAPI filters always run on an IIS server, filtering
every request until they find one they need to
process
• Mostly used for Authentication and Encryption of
the i/p or o/p data for a site locally or all the
apps globally

13. Application Pools
• Group of Web Applications and Web Sites are
called Application Pools
• Every application within an application pool
shares the same worker process
• The worker process(w3wp.exe) that services one
application pool is separated from the worker
process that services another
• Each separate worker process provides a process
boundary so each application pool is separated
by these process boundaries

14. IIS 6.0 Isolation Mode

15. Request Processing
• A request arrives at HTTP.sys.
• HTTP.sys determines if the request is valid. If the request is not
valid, it sends a code for an invalid request back to the client.
• If the request is valid, HTTP.sys checks to see if the request is
for static content (HTML) because static content can be served
immediately.
• If the request is for dynamic content, HTTP.sys checks to see if
the response is located in its “kernel-mode cache”.
• If the response is in the cache, HTTP.sys returns the response
immediately.
• If the response is not cached, HTTP.sys determines the correct
“request queue”, and places the request in that queue.

16. Request Processing
• If the queue has no worker processes assigned to it, HTTP.sys
signals the WWW service to start one.
• The worker process pulls the request from the queue and
processes the request, evaluating the URL to determine the
type of request (ASP, ISAPI, or CGI).
• The worker process sends the response back to HTTP.sys.
• HTTP.sys sends the response back to the client and logs the
request, if configured to do so.

17. And thus we welcome