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
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
If-Modified-Since: Tue, 12 Dec 2006 03:03:59 GMT
HTTP/1.1 304 Not Modified
How to configure ETag in IIS
In IIS. Goto WebSites -> Properties -> Http Headers ->Click on Add (Custom
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: