Section 2: The HTTP Conditional GET/Response Before performing the steps below, make sure your browsers cache is empty. (To do this under Firefox, select Tools->Clear Recent History and check the Cache box, or for Internet Explorer, select Tools->Internet Options->Delete File; these actions will remove cached files from your browsers cache.) Now do the following: 1) Start up your web browser, and make sure your browsers cache is cleared, as discussed above. 2) Start up the Wireshark packet sniffer 3) Enter the following URL into your browser http://gaia.cs.umass.edu/wireshark-labs/HTTP-wireshark-file2.html Your browser should display a very simple five-line HTML file. 4) Quickly enter the same URL into your browser again (or simply select the refresh button on your browser) 5) Stop Wireshark packet capture, and enter http in the display-filter-specification window, so that only captured HTTP messages will be displayed later in the packet-listing window.

Read Chapter 2.2.5 Web Caching and answer the following questions in your lab report:

1. Inspect the contents of the first HTTP GET request from your browser to the server. Do you see an IF-MODIFIED-SINCE line in the HTTP GET? 2. Inspect the contents of the server response. Did the server explicitly return the contents of the file? How can you tell? 3. Now inspect the contents of the second HTTP GET request from your browser to the server. Do you see an IF-MODIFIED-SINCE: line in the HTTP GET? If so, what information follows the IF-MODIFIED-SINCE: header? 4. What is the HTTP status code and phrase returned from the server in response to this second HTTP GET? Did the server explicitly return the contents of the file? Explain. 5. Export the second HTTP Get message.