Australian National University

First Semester Examination - June 2012

COMP2410 Networked Information Systems

Maximum marks: 60
Weight: 60% of the total marks for the course
Time allowed: 3 hours 15 minutes
Permitted materials:  None

Answer all questions.

Be precise. Avoid long-winded answers. Indicate clearly the question and part to which you are providing an answer.

There are five questions. All answers are to be submitted in plain text files found in directories named Q1 through Q5 in your home directory. You will need to enter the answers using an editor. Please remember to save the answers in the appropriate file. Save your changes frequently, so that you do not lose your work. Do not change the names of the directories or of the files.

Good luck!!!

Question 1 [10 marks]
Directory: Q1
File: Q1.txt

Answer all questions. Each question is worth 1 mark. Leave a blank line between answers. Write down the question number for the question alongside your answer.

  1. What does the Hop Limit field in an IPv6 address represent?
  2. How many bits will it take to represent the letters of the English alphabet a, b, ..., z?
  3. State two advantages of a centralized data processing facility.
  4. Which is the primary transport layer protocol used by SIP?
  5. The default port number for HTTPS is:
  6. What four bits of information uniquely identifies a tcp connection?
  7. Given the IPv4 address 192.168.1.12/26, what is its subnet mask?
  8. In the context of computer security, traffic analysis is an example of:
  9. When using IPSec, the encryption mode that provides protection for the entire IP packet is called:
  10. Which of the following is an algorithm for symmetric key cryptography?

Question 2 [12 marks]
Directory: Q2
File: Q2.txt

  1. Briefly describe three application areas for wireless LANs. [3 marks]
  2. What is packet switching? State two advantages of packet switching over circuit switching.. [3 marks]
  3. In the context of HTTP, differentiate between a proxy and a gateway. [3 marks]
  4. With respect to Quality of Service on the Internet, differentiate between elastic and inelastic traffic. Give an example of each. [3 marks]

Question 3 [15 marks]
Directory: Q3

Question 3a [3 marks]
File:Q3a.txt

You are given the following output of the command 'route -n': 

   Kernel IP routing table
   Destination     Gateway         Genmask         Flags Metric Ref  Use Iface
   192.168.2.0     0.0.0.0         255.255.255.0   U     0      0      0 eth0
   169.254.0.0     0.0.0.0         255.255.0.0     U     1000   0      0 eth0
   10.1.0.0        10.1.2.3        255.255.0.0     UG    100    0      0 eth1
   0.0.0.0         192.168.2.4     0.0.0.0         UG    100    0      0 eth0
Assume that the machine that this command is run on has IP address 192.168.2.220. Answer the following questions. Each question is worth 1 mark.
  1. Which interface will be used to send a packet to 192.168.2.26? Which router will be used?
  2. Which interface will be used to send a packet to 10.10.2.12? Which router will be used?
  3. Which interface will be used to send a packet to 172.168.1.63? Which router will be used?

Question 3b [4 marks]
File:Q3b.txt

Differentiate between the thick and thin client models of client-server applications. State two disadvantages of the thick client model.

Question 3c [8 marks]
File:Q3c.txt

Imagine that you are surfing the web using your favourite browser. You have come across this interesting link Lost in Cyberspace. You click the link and the page is downloaded to your machine. Describe, in the order that they occur, the steps involved in fetching the page. You only need to look at the events at the application and transport layers. Your machine, client1.anu.edu.au, is connected to a proxy server, proxy.anu.edu.au. The page that you are interested in is located on the machine originserver.com. See the diagram below. Assume that caching takes place on your machine and on the proxy server, and that the requested page is a static page, with an expiry date/time of Sat, 01 Dec 2012 16:00:00 GMT.

Question 4 [5 marks]
Directory: Q4
File: Q4.txt

Ubub Consultancy Services Limited (Ubub) is a hypothetical company providing computer software, services and training. Ubub is growing and needs a larger server. Imagine you are employed as a team member to upgrade the system. You look through the server logs to see which services are used most, so the system can be optimised. In the process you see some unauthorised access to a staff-only area. The server will need to be taken off-line for several hours to fix the problem. But your supervisor is worried about the outage, as this will result in a loss of business and reputation (Ubub has guaranteed there will never be an outage and agreed to pay compensation for any outage).

To help you, here is the ACS Code of Ethics:

  1. The Primacy of the Public Interest: You will place the interests of the public above those of personal, business or sectional interests.
  2. The Enhancement of Quality of Life: You will strive to enhance the quality of life of those affected by your work.
  3. Honesty: You will be honest in your representation of skills, knowledge, services and products.
  4. Competence: You will work competently and diligently for your stakeholders.
  5. Professional Development: You will enhance your own professional development, and that of your colleagues and staff.
  6. Professionalism: You will enhance the integrity of the Society and the respect of its members for each other.
Answer the following question:

Question 5 [18 marks]
Directory: Q5

Question 5a [6 marks]
File:Q5a.txt

  1. Bob wants to sign a message and send it confidentially to Alice. Describe how he would go about doing this using public key cryptography, as a sequence of steps. [3 marks]
  2. Now, implement the above procedure using gpg. The message can be found in the file message.txt. Bob's keys (public and private) can be found in the file bobs-keys.txt. Alice's keys (public and private) can be found in the file alices-keys.txt. You will need to import the keys into gpg, before you can use them for your purposes. The output of your operations will be a file called message.txt.gpg. As well, write down the commands that you used to do this, in the order in which they were executed. [3 marks]

Question 5b [12 marks]
File:Q5b.txt

Using wireshark, load the file tcpdump.out. This is a tcpdump of the output of a ping command. Only look at the entries from 4-33. Answer the following questions:

  1. What are the IP addresses of the source and destination machines in this ping? What is the domain name of the destination machine? [2 marks]
  2. What are the application and transport layer protocols used for the name server lookup? [1 mark]
  3. Which are the authoritative name servers for this domain (give the domain names and IP addresses)? [2 marks]
  4. How many echo requests have been sent? [1 mark]
  5. What is the network layer protocol used by ping? [1 mark]
  6. How many bytes of data per echo request? [1 mark]
  7. What is the round trip time, in milliseconds, of each of the echo requests? What is the average round trip time? [2 marks]
  8. What is the time to live of each echo request? [1 mark]
  9. What is the ethernet address of the source machine? How about that of the destination machine? [1 mark]