When an origin web server sends a response, the client's browser stores the response in its local cache. If the object has no expiration time, the browser makes subsequent requests for that content using a conditional GET request in the form of an extra request header field, such as If-Modified-Since. If the requested object is different than the content that the browser has cached, the origin web server sends a fresh copy of the object to the browser. Otherwise, the browser uses the object that is cached locally.
Although it is faster than serving the entire object each time the browser requests it, conditional GET requests can add up to a significant amount of traffic for your site. For example, if your site has several images for each page, clients might perceive a slow response time because of the large number of conditional GET requests for the image objects.
For this Intelligent Browser Referencing (IBR) example, you have three top-level nodes on the Policy Tree as follows:
For this example, your site serves a simple page that consists of two image files that appear as follows:<html> <head><title>example page</title></head> <body> <p>The images that your site serves:</p> <p><img src="myImages/image1.jpeg"></p> <p><img src="myImages/image2.jpeg"></p> </body> </html>
When the IBR tag (in this example, wa) is enabled, the WebAccelerator™ system modifies the page as follows:<html> <head><title>example page</title></head> <body> <p>The images that your site serves:</p> <p><img src="myImages/image1.jpeg;waRG2076ND"></p> <p><img src="myImages/image2.jpeg;wa7YW905BV"></p> </body> </html>
The IBR tag that the WebAccelerator system prepends to each image source URL, is a hash of the image that is stored in cache. In addition, the browser receives a long expiration time for each of the image files.
As a result, the client browser conducts subsequent requests for the page by:
If an image on the page is modified, the WebAccelerator system changes the IBR tag for the image and informs the client of the change. When the client performs a subsequent conditional GET request for the base page and receives the refreshed page, it compares the image, and notes the difference between image1.jpeg;wa4RR87M90 and image1.jpeg;waRG2076ND. This difference prompts the client to re-request the image from the WebAccelerator system.
For the General Options list, this table describes the Advanced settings and strings for IBR Options.
|IBR Prefix||;wa||Specifies a string that the WebAccelerator™ prepends to a unique value for
qualifying links or URLs embedded in your web pages.
Note: If you change the IBR prefix, F5 Networks® recommends thorough testing to ensure that your application functions properly.
|IBR Default Lifetime||182 Days||Specifies the lifetime for an Intelligent Browser Referencing (IBR) link or URL. Units of time range from Seconds through Months.|