Introduction

Internet Information Services (IIS) 7 provides a new request-processing architecture that

includes:

A new service, Windows Process Activation Service (WAS), which enables sites to use protocols other than HTTP and HTTPS.

A Web server engine that can be customized by adding or removing modules.

A new approach to processing requests, integrating the request-processing pipelines from IIS and ASP.NET.

This article describes the components, modules, and request-processing architecture in the

following sections:

IIS 7 Components Protocol Listeners

Hypertext Transfer Protocol Stack (HTTP.sys)

World Wide Web Publishing Service (WWW service)

Windows Process Activation Service (WAS)

IIS 7 Modules

Native Modules

Managed Modules

IIS 7 Request Processing

IIS 7 Application Pools

HTTP Request Processing in IIS 7

IIS 7 Components

IIS 7 contains several components that perform important functions for the application and Web

server roles in Windows Server® 2008 (IIS 7.0) and Windows Server 2008 R2 (IIS 7.5). Each

component has responsibilities, such as listening for requests made to the server, managing

processes, and reading configuration files. These components include protocol listeners, such as

HTTP.sys, and services, such as World Wide Web Publishing Service (WWW service) and Windows

Process Activation Service (WAS).

Protocol Listeners

Protocol listeners receive protocol-specific requests, send them to IIS for processing, and then

return responses to requestors. For example, when a client browser requests a Web page from

the Internet, the HTTP listener, HTTP.sys, picks up the request and sends it to IIS for processing.

Once IIS processes the request, HTTP.sys returns a response to the client browser.

By default, IIS 7 provides HTTP.sys as the protocol listener that listens for HTTP and HTTPS

requests. HTTP.sys was introduced in IIS 6.0 as an HTTP-specific protocol listener for HTTP

requests. HTTP.sys remains the HTTP listener in IIS 7, but includes support for Secure Sockets

Layer (SSL).

To support services and applications that use protocols other than HTTP and HTTPS, you can use

technologies such as Windows Communication Foundation (WCF). WCF has listener adapters that

provide the functionality of both a protocol listener and a listener adapter. Listener adapters are

covered later in this document. For more information about WCF, see Windows Communication

Foundation on MSDN.

Hypertext Transfer Protocol Stack (HTTP.sys)

The HTTP listener is part of the networking subsystem of Windows operating systems, and it is

implemented as a kernel-mode device driver called the HTTP protocol stack (HTTP.sys). HTTP.sys

listens for HTTP requests from the network, passes the requests onto IIS for processing, and then

returns processed responses to client browsers.

In IIS 6.0, HTTP.sys replaced Windows Sockets API (Winsock), which was a user-mode component

used by previous versions of IIS to receive HTTP requests and send HTTP responses. IIS 7

continues to rely on HTTP.sys for HTTP requests.

HTTP.sys provides the following benefits:

Kernel-mode caching. Requests for cached responses are served without switching to user mode.

Kernel-mode request queuing. Requests cause less overhead in context switching because the kernel forwards requests directly to the correct worker process. If no worker process is available to accept a request, the kernel-mode request queue holds the request until a worker process picks it up.

Request pre-processing and security filtering.

World Wide Web Publishing Service (WWW service)

In IIS 7, functionality that was previously handled by the World Wide Web Publishing Service

(WWW Service) alone is now split between two services: WWW Service and a new service,

Windows Process Activation Service (WAS). These two services run as LocalSystem in the same

Svchost.exe process, and share the same binaries.

Note   You may also see the WWW Service referred to as W3SVC in documentation.

How WWW Service works in IIS 6.0

In IIS 6.0, WWW Service manages the following main areas in IIS:

HTTP administration and configuration Process management

Performance monitoring

HTTP Administration and Configuration

The WWW Service reads configuration information from the IIS metabase and uses that

information to configure and update the HTTP listener, HTTP.sys. In addition, WWW service starts,

stops, monitors, and manages worker processes that process HTTP requests.

Performance Monitoring

The WWW Service monitors performance and provides performance counters for Web sites and

for the IIS cache.

Process Management

The WWW Service manages application pools and worker processes, such as starting, stopping,

and recycling worker processes. Additionally, the WWW Service monitors the health of the worker

processes, and invokes rapid fail detection to stop new processes from starting when several

worker processes fail in a configurable amount of time.

How the WWW Service works in IIS 7

In IIS 7, the WWW service no longer manages worker processes. Instead, the WWW Service is the

listener adapter for the HTTP listener, HTTP.sys. As the listener adapter, the WWW Service is

primarily responsible for configuring HTTP.sys, updating HTTP.sys when configuration changes,

and notifying WAS when a request enters the request queue.

Additionally, the WWW Service continues to collect the counters for Web sites. Because

performance counters remain part of the WWW Service, they are HTTP specific and do not apply

to WAS.

Windows Process Activation Service (WAS)

In IIS 7, Windows Process Activation Service (WAS) manages application pool configuration and

worker processes instead of the WWW Service. This enables you to use the same configuration

and process model for HTTP and non-HTTP sites.

Additionally, you can run WAS without the WWW Service if you do not need HTTP functionality.

For example, you can manage a Web service through a WCF listener adapter, such as

NetTcpActivator, without running the WWW Service if you do not need to listen for HTTP requests

in HTTP.sys. For information about WCF listener adapters and about how to host WCF applications

in IIS 7 by using WAS, see Hosting in WCF on MSDN.

Configuration Management in WAS

On startup, WAS reads certain information from the ApplicationHost.config file, and passes that

information to listener adapters on the server. Listener adapters are components that establish

communication between WAS and protocol listeners, such as HTTP.sys. Once listener adapters

receive configuration information, they configure their related protocol listeners and prepare the

listeners to listen for requests.

In the case of WCF, a listener adapter includes the functionality of a protocol listener. So, a WCF

listener adapter, such as NetTcpActivator, is configured based on information from WAS. Once

NetTcpActivator is configured, it listens for requests that use the net.tcp protocol. For more

information about WCF listener adapters, see WAS Activation Architecture on MSDN.

The following list describes the type of information that WAS reads from configuration:

Global configuration information Protocol configuration information for both HTTP and non-HTTP protocols

Application pool configuration, such as the process account information

Site configuration, such as bindings and applications

Application configuration, such as the enabled protocols and the application pools to which the applications belong

If ApplicationHost.config changes, WAS receives a notification and updates the listener adapters

with the new information.

Process Management

WAS manages application pools and worker processes for both HTTP and non-HTTP requests.

When a protocol listener picks up a client request, WAS determines if a worker process is running

or not. If an application pool already has a worker process that is servicing requests, the listener

adapter passes the request onto the worker process for processing. If there is no worker process

in the application pool, WAS will start a worker process so that the listener adapter can pass the

request to it for processing.

Note: Because WAS manages processes for both HTTP and non-HTTP protocols, you can run

applications with different protocols in the same application pool. For example, you can develop

an application, such as an XML service, and host it over both HTTP and net.tcp.

 

IIS 7 Modules

IIS 7 provides a new architecture that is different from previous versions of IIS. Instead of keeping

the majority of functionality within the server itself, IIS 7 includes a Web server engine in which

you can add or remove components, called modules, depending on your needs.

Modules are individual features that the server uses to process requests. For example, IIS uses

authentication modules to authenticate client credentials, and cache modules to manage cache

activity.

The new architecture provides the following advantages over previous versions of IIS:

You can control which modules you want on the server. You can customize a server to a specific role in your environment.

You can use custom modules to replace existing modules or to introduce new features.

The IIS 7 architecture also improves security and simplifies administration. By removing

unnecessary modules, you reduce the server's attack surface and memory footprint, which is the

amount of memory that server worker processes use on the machine. You also eliminate the

need to manage features that are unnecessary for your sites and applications.

Native Modules

The following sections describe the native modules that are available with a full installation of IIS

7. You can remove them or replace them with custom modules, depending on your needs.

HTTP Modules

Several modules in IIS 7 perform tasks specific to Hypertext Transfer Protocol (HTTP) in the request-

processing pipeline. HTTP modules include modules to respond to information and inquiries sent in

client headers, to return HTTP errors, to redirect requests, and more.

Module Name Description Resource

CustomErrorModuleSends default and configured HTTP error messages

when an error status code is set on a response.

Inetsrv\

Custerr.dll

HttpRedirectionMod

uleSupports configurable redirection for HTTP requests.

Inetsrv\

Redirect.dll

ProtocolSupportMod

ule

Performs protocol-related actions, such as setting

response headers and redirecting headers based on

configuration.

Inetsrv\

Protsup.dll

RequestFilteringMo

dule

Added in IIS 7.5. Filters requests as configured to

control protocol and content behavior.

Inetsrv\

modrqflt.dll

WebDAVModuleAdded in IIS 7.5. Allows more secure publishing of

content by using HTTP over SSL.

Inetsrv\

WebDAV.dll

Security Modules

Several modules in IIS 7 perform tasks related to security in the request-processing pipeline. In addition,

there are separate modules for each of the authentication schemes, which enable you to select modules

for the types of authentication you want on your server. There are also modules that perform URL

authorization, and a module that filters requests.

Module Name Description Resource

AnonymousAuthenticationModule

Performs Anonymous

authentication when no other

authentication method

succeeds.

Inetsrv\

Authanon.dll

BasicAuthenticationModule Performs Basic authentication.Inetsrv\

Authbas.dll

CertificateMappingAuthenticationMod

ule

Performs Certificate Mapping

authentication using Active

Directory.

Inetsrv\

Authcert.dll

DigestAuthenticationModulePerforms Digest

authentication.

Inetsrv\

Authmd5.dll

IISCertificateMappingAuthenticationM

odule

Performs Certificate Mapping

authentication using IIS

certificate configuration.

Inetsrv\

Authmap.dll

RequestFilteringModule

Performs URLScan tasks such

as configuring allowed verbs

and file name extensions,

setting limits, and scanning for

bad character sequences.

Inetsrv\

Modrqflt.dll

UrlAuthorizationModule Performs URL authorization.Inetsrv\

Urlauthz.dll

WindowsAuthenticationModulePerforms NTLM integrated

authentication.

Inetsrv\

Authsspi.dll

IpRestrictionModule

Restricts IPv4 addresses listed

in the ipSecurity list in

configuration.

Inetsrv\iprestr.dll

Content Modules

Several modules in IIS 7 perform tasks related to content in the request-processing pipeline. Content

modules include modules to process requests for static files, to return a default page when a client

doesn't specify a resource in a request, to list the contents of a directory, and more.

Module Name Description Resource

CgiModuleExecutes Common Gateway Interface (CGI)

processes to build response output.Inetsrv\Cgi.dll

DefaultDocumentMod

ule

Attempts to return a default document for requests

made to the parent directory.

Inetsrv\

Defdoc.dll

DirectoryListingModul

eLists the contents of a directory.

Inetsrv\

dirlist.dll

IsapiModule Hosts ISAPI extension DLLs. Inetsrv\Isapi.dll

IsapiFilterModule Supports ISAPI filter DLLs.Inetsrv\

Filter.dll

ServerSideIncludeMo

duleProcesses server-side includes code.

Inetsrv\

Iis_ssi.dll

StaticFileModule Serves static files.Inetsrv\

Static.dll

FastCgiModuleSupports FastCGI, which provides a high-

performance alternative to CGI.

Inetsrv\

iisfcgi.dll

Compression Modules

Two modules in IIS 7 perform compression in the request-processing pipeline.

Module Name Description Resource

DynamicCompressionMo

dule

Compresses responses and applies Gzip

compression transfer coding to responses.

Inetsrv\

Compdyn.dll

StaticCompressionModul

ePerforms pre-compression of static content.

Inetsrv\

Compstat.dll

Caching Modules

Several modules in IIS 7 perform tasks related to caching in the request-processing pipeline. Caching

improves the performance of your Web sites and Web applications by storing processed information,

such as Web pages, in memory on the server, and then reusing that information in subsequent requests

for the same resource.

Module Name Description Resource

FileCacheModule Provides user mode caching for files and file handles. Inetsrv\

Cachfile.dll

HTTPCacheModu

le

Provides kernel mode and user mode caching in

HTTP.sys.

Inetsrv\

Cachhttp.dll

TokenCacheMod

ule

Provides user mode caching of user name and token

pairs for modules that produce Windows user principals.

Inetsrv\

Cachtokn.dll

UriCacheModule Provides user mode caching of URL information.Inetsrv\

Cachuri.dll

Logging and Diagnostics Modules

Several modules in IIS 7 perform tasks related to logging and diagnostics in the request-processing

pipeline. The logging modules support loading of custom modules and passing information to HTTP.sys.

The diagnostics modules follow and report events during request processing.

Module Name Description Resource

CustomLoggingModule Loads custom logging modules.Inetsrv\

Logcust.dll

FailedRequestsTracingMo

duleSupports the Failed Request Tracing feature.

Inetsrv\

Iisfreb.dll

HttpLoggingModulePasses information and processing status to

HTTP.sys for logging.

Inetsrv\

Loghttp.dll

RequestMonitorModule

Tracks requests currently executing in worker

processes and reports information with

Runtime Status and Control Application

Programming Interface (RSCA).

Inetsrv\

Iisreqs.dll

TracingModuleReports events to Microsoft Event Tracing for

Windows (ETW).

Inetsrv\

Iisetw.dll

Managed Support Modules

A couple of modules in IIS 7 support managed integration in the IIS request-processing pipeline.

Module Name Description Resource

ManagedEngine

Provides

integration of

managed code

modules in the

IIS request-

processing

pipeline.

Microsoft.NET\Framework\v2.0.50727\

webengine.dll

ConfigurationValidationMo

dule

Validates

configuration

issues, such as

when an

application is

running in

Integrated mode

but has handlers

or modules

declared in the

system.web

section.

Inetsrv\validcfg.dll

Managed Modules

In addition to native modules, IIS 7 enables you to use managed code modules to extend IIS

functionality. Some of the managed modules, such as UrlAuthorization, have a native module

counterpart that provides a native alternative to the managed module.

Note   Managed modules depend on the ManagedEngine module.

The following table lists the managed modules that are available with a full installation of IIS 7.

For more information about the managed modules, see the .NET Framework SDK 2.0 on MSDN.

Module Name Description Resource

AnonymousIdentificat

ion

Manages anonymous

identifiers, which are

used by features that

System.Web.Security.AnonymousIdentificatio

nModule

support anonymous

identification such as

ASP.NET profile.

DefaultAuthenticatio

n

Ensures that an

authentication object

is present in the

context.

System.Web.Security.DefaultAuthenticationM

odule

FileAuthorization

Verifies that a user

has permission to

access the requested

file.

System.Web.Security.FileAuthorizationModule

FormsAuthentication

Supports

authentication by

using Forms

authentication.

System.Web.Security.FormsAuthenticationMo

dule

OutputCacheSupports output

caching.System.Web.Caching.OutputCacheModule

Profile

Manages user

profiles by using

ASP.NET profile,

which stores and

retrieves user

settings in a data

source such as a

database.

System.Web.Profile.ProfileModule

RoleManager

Manages a

RolePrincipal

instance for the

current user.

System.Web.Security.RoleManagerModule

Session Supports maintaining

session state, which

enables storage of

data specific to a

System.Web.SessionState.SessionStateModul

e

single client within

an application on the

server.

UrlAuthorization

Determines whether

the current user is

permitted access to

the requested URL,

based on the user

name or the list of

roles of which a user

is a member.

System.Web.Security.UrlAuthorizationModule

UrlMappingsModule

Supports mapping a

real URL to a more

user-friendly URL.

System.Web.UrlMappingsModule

WindowsAuthenticati

on

Sets the identity of

the user for an

ASP.NET application

when Windows

authentication is

enabled.

System.Web.Security.WindowsAuthentication

Module

 

IIS 7 Request Processing

In IIS 7, the IIS and ASP.NET request pipelines combine to process requests with an integrated

approach. The new request-processing architecture consists of an ordered list of native and

managed modules that perform specific tasks in response to requests.

This design provides several benefits over previous versions of IIS. First, all file types can use

features that were originally available only to managed code. For example, you can now use

ASP.NET Forms authentication and Uniform Resource Locator (URL) authorization for static files,

Active Server Pages (ASP) files, and all other file types in your sites and applications.

Second, this design eliminates the duplication of several features in IIS and ASP.NET. For

example, when a client requests a managed file, the server calls the appropriate authentication

module in the integrated pipeline to authenticate the client. In previous versions of IIS, this same

request would go through an authentication process in both the IIS pipeline and in the ASP.NET

pipeline.

Third, you can manage all of the modules in one location, instead of managing some features in

IIS and some in the ASP.NET configuration. This simplifies the administration of sites and

applications on the server.

IIS 7 Application Pools

Application pools separate applications by process boundaries to prevent an application from

affecting another application on the server. In IIS 7, application pools continue to use IIS 6.0

worker process isolation mode. In addition, you can now specify a setting that determines how to

process requests that involve managed resources: Integrated mode or Classic mode.

Note: In IIS 6.0, worker process isolation mode and IIS 5.0 isolation mode are set at the server

level. This makes it impossible to run both isolation modes on the same server. However, in IIS 7,

Integrated mode and Classic mode are set at the application pool level, which enables you to run

applications simultaneously in application pools with different process modes on the same server.

Integrated application pool mode

When an application pool is in Integrated mode, you can take advantage of the integrated

request-processing architecture of IIS and ASP.NET. When a worker process in an application pool

receives a request, the request passes through an ordered list of events. Each event calls the

necessary native and managed modules to process portions of the request and to generate the

response.

There are several benefits to running application pools in Integrated mode. First the request-

processing models of IIS and ASP.NET are integrated into a unified process model. This model

eliminates steps that were previously duplicated in IIS and ASP.NET, such as authentication.

Additionally, Integrated mode enables the availability of managed features to all content types.

Classic application pool mode

When an application pool is in Classic mode, IIS 7 handles requests in the same way as in IIS 6.0

worker process isolation mode. ASP.NET requests first go through native processing steps in IIS

and are then routed to Aspnet_isapi.dll for processing of managed code in the managed runtime.

Finally, the request is routed back through IIS to send the response.

This separation of the IIS and ASP.NET request-processing models results in duplication of some

processing steps, such as authentication and authorization. Additionally, managed code features,

such as Forms authentication, are only available to ASP.NET applications or applications for which

you have script mapped all requests to be handled by aspnet_isapi.dll.

Be sure to test your existing applications for compatibility in Integrated mode before upgrading a

production environment to IIS 7 and assigning applications to application pools in Integrated

mode. You should only add an application to an application pool in Classic mode if the application

fails to work in Integrated mode. For example, your application might rely on an authentication

token passed from IIS to the managed runtime, and, due to the new architecture in IIS 7, the

process breaks your application.

HTTP Request Processing in IIS 7

IIS 7 has a similar HTTP request-processing flow as IIS 6.0. The diagrams in this section provide

an overview of an HTTP request in process.

The following list describes the request-processing flow that is shown in Figure 1:

1. When a client browser initiates an HTTP request for a resource on the Web server, HTTP.sys intercepts the request.

2. HTTP.sys contacts WAS to obtain information from the configuration store.

3. WAS requests configuration information from the configuration store, applicationHost.config.

4. The WWW Service receives configuration information, such as application pool and site configuration.

5. The WWW Service uses the configuration information to configure HTTP.sys.

6. WAS starts a worker process for the application pool to which the request was made.

7. The worker process processes the request and returns a response to HTTP.sys.

8. The client receives a response.

Figure 1: Overview of an HTTP Request

In a worker process, an HTTP request passes through several ordered steps, called events, in the

Web Server Core. At each event, a native module processes part of the request, such as

authenticating the user or adding information to the event log. If a request requires a managed

module, the native ManagedEngine module creates an AppDomain, where the managed module

can perform the necessary processing, such as authenticating a user with Forms authentication.

When the request passes through all of the events in the Web Server Core, the response is

returned to HTTP.sys. Figure 2, below, shows an HTTP request entering the worker process.

 Figure 2: Detail of a HTTP request inside the Worker Process

Tools for Troubleshooting IIS 6.0 (IIS 6.0)Good tools are an indispensable part of any troubleshooting effort. This section identifies tools that you

can use to help troubleshoot problems that you encounter on applications running on IIS 6.0. It also

provides tips for getting the most benefit from each tool. Specific tool usage scenarios are also discussed

in this section.

The following tools are useful for troubleshooting problems that occur with IIS 6.0:

• WFetch (WFetch.exe). This tool allows you to generate customized HTTP requests and view request

and response data.

• File Monitor (FileMon.exe). This tool allows you to view and capture real-time file system activity.

• Registry Monitor (RegMon.exe). This tool allows you to view and capture real-time system registry

activity.

• IIS Request Monitor. This tool captures information about HTTP requests in IIS worker processes,

which can help you isolate and understand problems when worker processes become slow or

unresponsive.

• Secure Socket Layer (SSL) Diagnostic Tool (SSLDiag). This tool helps you identify configuration

problems in the IIS metabase, certificates, or certificate stores when running Web sites that use SSL.

• Authentication and Access Control Diagnostics (authdiag.exe). This tool allows you to review, test,

and correct problems with authentication and authorization.

• IIS 6.0 Enterprise Tracing for Windows. This tool allows you to trace HTTP requests as they move

through various components in your server architecture. IIS components provide informational events

and error events (if applicable) to the ETW architecture as requests enter and exit each component.

You can view the event data to see exactly where in the IIS architecture a request failed or became

unresponsive.

• Network Monitor. This network tracing utility allows you to view activity in the network stack. Network

Monitor is included with Windows Server 2003.

• System Monitor. This tool allows you to view and collect system performance data. System Monitor is

included with Windows Server 2003.

• HRPlus. This tool provides error lookup functionality.

• Microsoft Debugging Tools for Windows. This tool allows you to debug and diagnose application

problems.

IIS Fundamentals (IIS 6.0)IIS is an HTTP protocol server, which means that it accepts and replies to HTTP requests. IIS processes three

types of HTTP requests:

• Static content (like HTM document) requests

• CGI requests

• ISAPI requests

By understanding the fundamentals of IIS architecture and the related functionality, you can discover and

isolate problems much more quickly. You will also be better equipped to differentiate between real problems

and expected behavior.

This section explores the following functionality, which any IIS troubleshooter must understand:

• HTTP Protocol Basics: Explains the way Internet browsers and servers running IIS communicate with each

other.

• IIS Service Startup: Sometimes problems arise even before IIS starts servicing requests. This section

describes the startup process and typical startup behavior, which can help you determine the causes of

problems.

• HTTP Request Walkthrough: Explains the various phases that a typical request passes through as it

moves through the service.

HTTP Status Codes in IIS 6.0 (IIS 6.0)HTTP status codes provide the best information about what is happening with IIS. On an active Web server,

HTTP status codes provide a continuous feed of up-to-the-moment information about the activity and health

of the server.

Most HTTP status codes have three digits, for example, 401. Some status codes have three digits followed by

a decimal point, and one or two more digits (for example, 300.12). In such a case, the number that follows

the decimal point is called the substatus code.

Codes within each hundred-number range provide specific types of information, as summarized in

Table 11.2 HTTP Status Codes.

Table 11.2 HTTP Status Codes

Status Code Range

Type of Code

100 Informational

200 Successful

300 Redirection

400 Client Error

500 Server Error

As an administrator, at some point you will inevitably need to determine which HTTP status codes are being

returned by IIS. There are a number of ways to do this. Your choice of method depends on the amount of

information that you need and the type of problem that you are troubleshooting. If you have a problem that

is limited to one or a few clients, viewing the status codes from the clients Web browser or issuing a

reproduced HTTP request with WFetch might best serve your needs. However, if you need to look for an

individual request or for a collection of multiple requests over a period of time, you should examine the IIS

logs. Viewing IIS logs allows you to see not only the main HTTP status code, but the Win32 error code and

the HTTP substatus code (if logging is configured to do so). The Win32 error codes and the HTTP substatus

codes often contain information that is critical to your troubleshooting effort.