Purpose of the lab is to continue to develop your understanding of network communications by looking deeper into the network packets used to connect to a distant server. The primary activities of the lab focus on the capture and examination of the network protocols in layer 3 & 4 of the OSI reference model. That is the Internet Protocol and Transmission Control Protocol sections shown in Figure 1.

As in other labs you should set up the lab by explain how this lab fits into the reading and with other labs. Provide a brief overview of each of the main sections of the lab. As before, provide a complete list of hardware and software used in this lab.

Overall Objectives for this Lab

1. Get an overview of how layers 2 & 3 of the OSI protocol stack interact to facilitate communications between endpoints of a conversation.

2. Identify the specific role of the IP protocol in end-to-end communications

3. Examine how layers 3 & 4 interact in your communication with the web server.

4. Identify the call setup, transmission and the call termination accomplished in layer 4 protocols. Specifically we are interested in TCP as a layer 4 protocol in this lab

5. Explore the HTTP protocol conversation between your PC and a Web site with the view of seeing how TCP/IP facilitates that communication

Lab Write up

( Part A: Internet Protocol

In this section of the lab you are going to explore a little deeper into the Ethernet packet. You may recall that the IP Protocol is a layer 3 protocol, and that it is used to guide packets between networks. Your write-up of this section should explain how the IP protocol is employed within the packet to help guide it between networks. In particular, the questions below are focusing on packets sent across the Internet to a server in some other location.

Explain in some detail how the IP protocol assists in the packet navigation across the Internet. You will want to reference the idea of the datagram service of the IP protocol. You will need to reference instructor slides and tutorials from this section and other resources to support your analysis. To help you get started with this analysis I have included some questions below to help you think about the role of the IP Header of the packet (See Figure 2). Your narrative about what you learn could include answers to some of these topics

· The IP header has multiple information fields. What are they used for?

· How do these header attributes insure packets are sent and received successfully?

· How does the definition of a datagram help explain the function of the IP header?

( Part B: TCP Protocol

Transmission Control Protocol is one of the Layer 4 protocols used to communicate across the network. TCP is used to establish a reliable connection to a host on the far end of the conversation. The reliable connection creates addition traffic when sending acknowledgements of received packets. It makes sense that we would want to have a reliable connection, but there are times when this extra overview is not helpful. For example, when sending voice over IP we can’t resend packets that may have been lost because of the timing and the need to get all packets in order make resending lost packets impractical. For these types of applications we use UDP , rather than TCP as the Layer 4 protocol.

In this section of the lab you will explore information found in layer 4 of the packets you captured to learn something about how the layer 4 protocols provide for a reliable end-to-end communication service. To help direct your efforts the questions below might be helpful.

· Review the reading on TCP & UDP in your book and perhaps look at other resources to help you explain the differences between TCP & UDP. They are both layer protocols, but they serve different purposes. What are the differences? ( Hint: Use UDP as your packet filter value to see what you get. The information at http://en.wikipedia.org/wiki/User_Datagram_Protocol might prove useful in this discussion.

· What are the field in the TCP header used for, and how do they help in setting up a reliable end-to-end communication (aka connection-oriented connection)?

· Explain the use of port numbers in layer protocols. How are this port numbers used with the IP address to establish the right connection between programs on both ends of the ‘conversation’? What are well-known port numbers? What about the other port numbers not listed there?

· Define any new words or acronyms and highlight them to your running glossary

Conclusion

Address the following topics from your experience in the lab…..

1) What were the most important concepts you learned in this lab?

2) What did you discover in the process of exploring the contents of a packet?

3) As a network administrator, how might this information be useful to you?

4) How does this lab relate to the reading?

References

APA Format

Glossary

(start with previous lab Glossary entries)

Figure 1: Wireshark Protocol Capture Window

IP Packet Header Section

Figure 2: IP Header

Figure 3: TCP Header

Page 2 of 5