Configuring ETags in IIS7

Entity tags (ETags) are the mechanism web servers and browsers use to determine whether an element in the browser cache matches the object on the server.

Since ETags are as a rule built using attributes that make them unique to the particular server the site is hosted on, the tags will not match when the browser gets the original component from one server and then tries to validate that component on another server.

ETags are configured in the Internet Information Services (IIS) manager.

Since ETags is added to the headers the server sends to the client (Response headers), we are interested in the corresponding item:

Create a new header:

Name it ETags:

As an option you can add them right into web.config in the system.webServer section:

<system.webServer>
   ...
        <httpProtocol>
            <customHeaders>
                <add name="ETag" value="""" />
            </customHeaders>
        </httpProtocol>
   ...
</system.webServer>

That is all. ETags will appear in the headers.