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The Australian National University

Laboratory 5 - TCP/IP and Ethernet

Aim

The aim of this lab is to discuss the material covered in the lectures on wireless networks and tcp/ip. It also gives you some hands on experience with using some networking tools to help you better understand the material.

Discussion

Preparation

Please go through the slides for the lectures on wireless networks and tcp/ip. As well, go through pages 223-225, 234-238 and 240-249 (Chapter 6, Wireless LANs 1); 269-280 and 289-299 (Chapter 7, Wireless LANs 2); 303-334 (Chapter 8, TCP/IP 1); 341-345 (Chapter 9, TCP/IP 2). Note down any questions that you may have and bring it up at the end of the discussion session.

  1. Would you use the 2.4GHz or 5GHz band at home, for wireless LANs? Why?
  2. What is an ESS? What happens when you roam?
  3. How does CSMA/CA+ACK work? What makes it a reliable protocol?
  4. Differentiate between the three modes of operation in Bluetooth 4.0.
  5. Discuss one application area of NFCs.
  6. Why would you need the 802.1X mode of operation for 802.11i, in large organizations?
  7. Why does DNS use UDP and not TCP as the transport layer protocol?
  8. What does the subnet mask tell you? Why didn't you need one for classful addressing?
  9. How does a router using its routing table?
  10. Why is NAT required? What are some of its drawbacks?

Linux Networking Commands

Run the following commands:

route

route -n
How many interfaces are there? Do you understand the different parts of the output? Use the man page to figure out the output.

ping

ping cs.anu.edu.au
What can you use this command for? What information does the output of the command give you? Try the same again, with the destination being a URL outside of ANU. What happens?

traceroute

traceroute cs.anu.edu.au
Try the same again, with the destination being a URL outside of ANU. What happens?

wireshark

Wireshark is a software tool for capturing and analyzing network packets. It is installed on the student system. In order to use wireshark to capture packets, you need root privileges. What we will do instead is give you a file containing the information from captured packets.

Save the file tcpdump.out in your local directory. Run wireshark, by running the following command from the terminal: 

    wireshark
Use wireshark to open the file tcpdump.out and examine the output. Click the mouse on each line of displayed text in the upper window and see what happens. Try and understand the information that is being shown. In particular, observe the DNS requests, the TCP handshake and the start and end of the HTTP information. What is the IP address of the DNS server? Use dig to find its domain name. What version of http is being used?

Use the Expand All option under View to get more information. Use the different options under Analyze and Statistics and see what you get. When you are done, quit wireshark.

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