title: cache-control:max-age=0 and If-Not-Modified in http request
body: <p>Our site uses akamai as its CDN.  Since there is browser cache, after cache  expires in browser, it will send <code>cache-control:max-age=0</code> and <code>If-Not-Modified</code> in the http request which will get a 304 response.(I think this 304 is retured from origin web server)</p>
  
  <p><code>cache-control:max-age=0</code> will force CDN forward this http request to the origin web server, so why do we need a CDN?</p>
  
  <p>I am not sure which type of http reuqest is served by CDN...and how CDC keep update with origin server?</p>