DOCUMENT:Q247404  03-DEC-2000  [iis]
TITLE   :How to Modify the Cache-Control HTTP Header When You Use IIS
PRODUCT :Internet Information Server
PROD/VER::5.0
OPER/SYS:
KEYWORDS:

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The information in this article applies to:

 - Microsoft Internet Information Services version 5.0 
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SUMMARY
=======

Web administrators who use Internet Information Services (IIS) may need to
periodically disable the caching of content that changes frequently. This
article describes how to set the value of the Cache-Control HTTP Header by using
Active Server Pages (ASP), as well as the metabase property CacheControlCustom.

MORE INFORMATION
================

When you work with content that often changes, you may want to specify what
content can be cached and what cannot, and if the client or a proxy server
should cache the content. You can specify these options in IIS through the
CacheControlCustom property, which can be set for the entire server, a
particular Web site, or a specific physical or virtual directory. Setting this
property returns HTTP headers that resemble the following:

   HTTP/1.1 200 OK
   Server: Microsoft-IIS/5.0
   Cache-Control: <CACHE SETTING>
   Content-Type: <type>/<subtype>
   Content-Length: <size of content>

The cache setting value is determined by the HTTP/1.1 specification.

Commonly-Used HTTP/1.1 Cache-Control Header Values
--------------------------------------------------

The HTTP/1.1 specification in RFC 2616 defines several values for the
Cache-Control header. The following list contains a few of the more common
values that are used.

 - Public: The HTTP response may be cached by any cache. For example, either a
   client or a proxy server can cache the response. This allows sharing of
   content across users who are using the same proxy server.

 - Private: The response message is intended for a single client and must not be
   cached by a shared cache. For example, a proxy server should not cache the
   response even though a client can. This allows the client to maintain a
   cached version, while other clients that are using the same proxy server
   maintain different cached versions.

 - No-cache: No cache in the entire path should maintain a cached copy of the
   response. This allows you to specify that neither the client or proxy server
   will respond to a subsequent content request by using a cached version.

Setting the Cache-Control Property
----------------------------------

The following examples define different methods for setting this value:

For a Page:

Using Active Server Pages (ASP), the following ASP code disables caching of a
particular page:

   <% @Language="VBScript" %>
   <% Response.CacheControl = "no-cache" %>

NOTE: This code must be inserted at the beginning of the page, unless buffering
is enabled, because it is modifying the HTTP headers.

For a Folder:

The following examples set the Cache-Control setting for a folder or virtual
directory named "Images" in the default Web site:

 - Using Adsutil.vbs:

   1. Open a command prompt and change to your C:\InetPub\AdminScripts folder.

   2. Run the following command:

   CSCRIPT ADSUTIL.VBS SET W3SVC/1/ROOT/images/CacheControlCustom "no-cache"

 - Using ADSI Scripting:

   1. In Notepad, enter the following ADSI code:

   Option Explicit
   Dim objCache
   Set objCache = GetObject("IIS://localhost/w3svc/1/root/images")
   objCache.CacheControlCustom = "no-cache"
   objCache.SetInfo

   2. Save the file as Disablefolder.vbs in your C:\InetPub\AdminScripts folder,
      and then close Notepad.

   3. At a command prompt, change to your C:\InetPub\AdminScripts folder.

   4. Run the following command:

   CSCRIPT DISABLEFOLDER.VBS

REFERENCES
----------

For more information on this topic, please see the following Microsoft Knowledge
Base article:

   Q247389 IIS: How to Disable Caching of Specific MIME Types

In addition, see section 14.9 of the HTTP/1.1 specification in RFC 2616 at the
following URL:

   RFC 2616 Hypertext Transfer Protocol -- HTTP/1.1

Additional query words: iis5 iis5.0

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Keywords          :  
Technology        : kbiisSearch kbiis500
Version           : :5.0
Issue type        : kbhowto

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