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How to configure ETag in IIS 6.0

Posted by Raja Krishnamurthy Articles | Networking April 08, 2011
Entity tags (ETags) are a mechanism that web servers and browsers use to determine whether the component in the browser's cache matches the one on the origin server.
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What is ETag(Yahoo)

Entity tags (ETags) are a mechanism that web servers and browsers use to determine whether the component in the browser's cache matches the one on the origin server. (An "entity" is another word a "component": images, scripts, stylesheets, etc.) ETags were added to provide a mechanism for validating entities that is more flexible than the last-modified date. An ETag is a string that uniquely identifies a specific version of a component. The only format constraints are that the string be quoted. The origin server specifies the component's ETag using the ETag response header.

HTTP/1.1 200 OK
Last-Modified: Tue, 12 Dec 2006 03:03:59 GMT
ETag: "10c24bc-4ab-457e1c1f"
Content-Length: 12195

Later, if the browser has to validate a component, it uses the If-None-Match header to pass the ETag back to the origin server. If the ETags match, a 304 status code is returned reducing the response by 12195 bytes for this example.

GET /i/yahoo.gif HTTP/1.1
Host: us.yimg.com
If-Modified-Since: Tue, 12 Dec 2006 03:03:59 GMT
If-None-Match: "10c24bc-4ab-457e1c1f"
HTTP/1.1 304 Not Modified

How to configure ETag in IIS

In IIS. Goto WebSites -> Properties -> Http Headers ->Click on Add (Custom Http Header)

ETag1.gif

In Custom Header Name specify "Etag"

Leave Custom Header Value as blank.

Click Ok. It would check all your virtual directories which have HTTP Headers and you can select which all you want to configure Etag. Given below is the picture after such configuration:

ETag2.gif

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