Unless the assignment says otherwise, all answers are limited to 50 words. Longer answers will not be graded. Assignments are due at the start of class. Please submit them using email to So that we don’t all share infections, please don’t use email attachments.

Assignment 1

1. Which is better, circuit switching or packet switching?  Why?

2. Read all of the site,  Under what circumstances is  late homework accepted?  When is the date when you must have a project topic that has been accepted by the professor?

3. How does the value of a network vary as the number of participants increases?  Why?

4. What is the Internet?

5. Suppose the Internet has not been invented yet but everyone wants one, so you are in charge of the design. The first question that you are asked is about addressing. What will you need to have addresses for? Which of these addresses should be fixed in hardware and which can be changed by an administrator?

6. Install Wireshark on a computer that you will be using for class, and submit a screenshot of an Ethernet frame captured by Wireshark.  Explain what the screenshot shows.

Assignment 2

1. How does an Ethernet switch differ from an Ethernet hub?

2. Why are network systems layered?

3. What happens if we increase the number of hosts in an Ethernet beyond 1024?  Why?

4. What is the difference in terms of network traffic between two Ethernet segments connected by a bridge and two segments connected by an adaptive bridge?  Why?

5. Layering is found in many processes that we deal with.  Describe the process layering that is present at GWU, with yourself taking this course as the ultimate consumer, at the highest level.  You may use 100 words to answer this question!

6. What is the Good Citizen Principle?

7. What is the most critical resource on the Internet?

8. Read RFCs 2324 and 2325.  Why are they important?

Assignment 3

1. Comer 5.6

2. Comer 5.9

3. Comer 6.4

4. Comer 6.6

5. Comer 6.7

6. In NDP,  how does a host discover routers on the network?  Where did you get this information?

Assignment 4

1.  Run Ping for, and and explain the results for each one.  Note that if you get different results, you need to explain why you are getting these differences.  Explain the reasons for the results that you obtain for each ping.

2. Which ICMP messages does ping use, and just how does it use them?

3. Run traceroute for the three sites in problem 1, and explain the results.  Again, an explanation is needed for each result.

4. Traceroute uses 2n messages each time it’s run; find an experimental traceroute that uses fewer messages and explain how it works.

5. Using Wireshark, capture the messages that are interchanged in one of the traceroute interactions and show them so that I can read them.  Explain what is happening.

5. Comer 7.1

6. Fragmentation and reassembly are different for IPv4 and IPv6.  Which is better?  Why?

7. Comer 8.4

Assignment 5

1. Describe how to use ICMP to synchronize the clocks at two different servers that are on different networks.

2. Suppose that I have decided to use UDP to transfer data to my application.  My application needs to receive the data in the order it was transmitted.  Will this be a problem with UDP?  If it is, how can I solve the problem?

3. What kinds of applications cannot run through a NAT box?

4. Can a local address in a network behind a NAT box be the same as a globally unique address?  Explain.

5. What are the IP addresses that are reserved for use by private networks?  What is the IP address for your own PC?  Is it one of these addresses?  Why or why not?

6. Comer 10.2

7. Comer 10.3

8. Comer 11.1

Assignment 6

  1. Carry out problem 3 of Assignment 4. Explain the results by discussing how many hops it took to reach various sites and why, and explain differences in elapsed time to reach the various sites. When did the datagram leave the home ISP and enter an exchange point, or some other network that connects autonomous systems? Which company’s networks were used? Why are the results as they are in each case? Be sure to include,,, and in the hosts you test, in addition to the originally required host names.  You may use 100 words for your answer to this question.
  2. Your new boss has asked you to recommend the default initial TTL setting for your network.  Conduct a series of experiments to determine what that value should be.  Summarize your data and give your recommendation.
  3.  Layering is perhaps the most crucial principle in the design of communication protocols, but it’s not unique to communications.  As an illustration of this, choose some process that you engage in regularly or that you observe in society, and describe the process layering that takes place.  An example would be the process layering that takes place between me and a Web marketing client; they engage me and pay me, and look at results that I produce in terms of increased business.  I do all sorts of technical things with their site that they don’t have to get involved with, things that bring more visitors to their site.  The top layer might be the client layer and the bottom layer the worker layer.  Choose some example different from this one, different from the previous assignment, that has several layers of process, and describe the process layers and some associated events.
  4. Comer 12.2
  5. Comer 13.9
  6. If an IPv4 router finds that it needs to fragment a datagram that it is sending, and the “do not fragment” bit is set in the datagrams’s header, what does it do?
  7. Recall that there is a reserved port Echo Reply in UDP.  Should traceroute be implemented using ICMP or using UDP?  Why?  What are the tradeoffs?  Which protocol is usually used for traceroute?
  8. Has RFC 1393 been widely implemented?  How do you know?  How did you find this information?

Assignment 7

1. Does a multicasting router need to know how many subscribers are on a network that it connects to for a multicast group?  Explain.

2. Describe the efficiency gains of MPLS in terms of forwarding equivalence classes (FECs).  Hint:  check the RFC.  What is a practical analogy that describes an FEC?

3. Can there be more than one FEC for a single LSR?  Can there by more than one LSR for a single FEC?  Hint:  check the RFC

4. Comer 14.5

5. Comer 16.7

Assignment 8

  1. Run traceroute to, and  Capture datagrams from traceroute using WireShark.  What protocols are used?  Show Wireshark results that illustrate which protocols are used by traceroute.

2.  What are the two types of IGP, and how do they compare?  Which one of them appeals most to you, and why?

3. Comer 19.2

4. Comer 19.3

5. Comer 19.7

Assignment 9

  1.  What is RLNC?  How does it work?

2. Use Wireshark to capture a DNS lookup as part of an SMTP activity.  Put this into your homework submission and briefly explain what’s happening.

3. Moses needed 10 commandments, but that covered all of life.  To simply design Internet protocols, we can get by with five.  Write the Five Commandments of Internet Protocol Design.  Each one starts with “Thou shalt”  or “Thou shalt not”.

4. Comer 24.14

5. (Optional)  Use TELNET to connect to the SMTP server and send an email message to the professor (at from Hillary Clinton at apologizing for not winning the recent Presidential election, and thanking the professor for his support.  Show the entire SMTP dialogue.  Be sure the email mentions your own name so that the professor can tell who actually wrote it.

Assignment 10

Note:  for this assignment, you are encouraged to use the class email address to share information about port numbers and DNS addresses to use for problem 1.

1. Use Wireshark to capture SMTP negotiation sessions, put screenshots of those sessions into your homework submission, and explain them.  Be sure the dialogue in the sessions is readable.  You don’t have to include the entire Wireshark screen.


3. Use Wireshark to capture a DHCP dialogue.  Determine the length and type of your computer’s lease on its IP address.  Show the Wireshark capture of the message containing the type and length of the lease.

Assignment 11

1. Use TELNET to send a test email message to  The email is to be from President Obama, and the return address is to be  The message sent is to include your name, so that I can verify that you’ve successfully send the email.  Save the dialogue, put it into your homework submission and explain it.

2. Use Wireshark to capture SMTP negotiation sessions from problem 1, put screenshots of those sessions into your homework submission, and explain them.  Be sure the dialogue in the sessions is readable.  You don’t have to include the entire Wireshark screen.

3. Use Wireshark to capture a DNS lookup as part of an SMTP activity.  Put this into your homework submission and explain it.