Right-click the text file and select Properties.

Defining Networks with the OSI Model | 43 This is a secure, encrypted connection to the PayPal Web site. Many Web sites offer this, not only when actual transactions are made, but also as a courtesy to customers, giving them peace of mind in that their entire session with the Web site is encrypted and somewhat secure. This type of encryption protocol works on port 443, and the actual transmission of encrypted data is governed by the presentation layer. One of a few protocols can be used during HTTPS transfers. The most common example as of the writing of this book is Transport Layer Security TLS, but you might also see Secure Sockets Layer SSL. Data that is transferred over the web is usually compressed, or encoded, as well. For example, many web browsers accept gzip encoding. DEFINE THE APPLICATION LAYER GET READY. Layer 7—the application layer—is where protocols like HTTP, FTP, and POP3 reside. The application layer is not the applications themselves Internet Explorer or Outlook, but rather the protocols that the applications initiate, such as HTTP or POP3. For example, when you open Internet Explorer, you are opening an application. If you were to type http:www.microsoft.com in the URL field and press Enter, doing so would initiate the HTTP protocol starting the transfer of data over the OSI model, beginning with the applica- tion layer. Let’s capture some data as we connect to a Web site by performing the following actions:

1. Open Wireshark and begin a packet capture.

2. Connect with your browser to www.microsoft.com.

3. Stop the capture and view the information.

4. Look for the first HTTP packet in the Protocol column. This should be called GET

HTTP1.1 in the Info column.

5. Click the packet and drill down through the various layers in the middle pane. Not

only will you see Layers 2 and 3 as we defined them in the network layer section, but you will also see the upper layers in action. Your results should be similar to Figure 2-7. Figure 2-7 Wireshark capture of an HTTP packet

6. Click the ⫹ sign next to Hypertext Transfer Protocol. Here, you will see the host

that you connected to: www.microsoft.com. You will also notice the gzip and deflate encodingdecoding schemes we alluded to earlier.