Computer Networks

Tutorial #7

1. The following are some (possibly hypothetical) IP addresses:

   205.184.10.20	139.130.17.42	138.80.128.18
   10.170.45.56	149.144.20.82	192.54.252.7
   

   Extract the network number and the host number from each of these, stating what class of network it is.

2. What do you think is the origin of the term datagram?

3. Why must a router always have at least two different IP addresses?

4. What¹ is the chief difference between the IP addressing scheme and the International (and Australian) telephone numbering scheme?

5. La Trobe University, Bendigo, has a class-B network (149.144.0.0). Using some (very rough) "back of the envelope" calculations, estimate whether a class-C network would have been sufficient.

6. One of the weaknesses of the IP addressing scheme is that when a machine is physically moved from one network to another, its address must change. Why is this so, and why is it a problem?

7. What is UDP? In the lecture. some examples where UDP is useful were given. However, one of the appropriate uses of UDP occurs in multi-player (networked) games. Why is it likely to be particularly appropriate in this application?

8. What are the three characteristics of datagram delivery in the Internet?

9. Consider² a machine with two physical network connections, and two IP addresses, I(1) and I(2). Is it possible for that machine to receive a datagram destined for I(2) over the network with address I(1)? Explain.

10. Is³ it possible to address a datagram to a router's (IP gateway's) IP address? Does it make sense to do so?

11. The following is the output of a run of the traceroute command, "looking from" outside La Trobe back towards Bendigo. It was, in fact, run on a Unix system called morinda in the School of IT at NTU in Darwin.

    morinda> traceroute ironbark.bendigo.latrobe.edu.au
        [....six lines deleted]
     6  nsw-vic.atm.net.aarnet.edu.au (192.12.76.2)  79 ms  79 ms  79 ms
     7  vic-gw.vrn.EDU.AU (203.21.130.162)  80 ms  80 ms  87 ms
     8  latrobe-gw.vrn.EDU.AU (203.21.130.133)  81 ms  83 ms  80 ms
     9  r-elt-fddi.latrobe.edu.au (131.172.20.8)  80 ms  81 ms  80 ms
    10  r-bgoatm34-atm.latrobe.edu.au (131.172.239.5)  81 ms  328 ms  84 ms
    11  busfddi0.bendigo.latrobe.edu.au (149.144.10.1)  81 ms  81 ms  81 ms
    12  ironbark.bendigo.latrobe.edu.au (149.144.21.60)  81 ms  81 ms  81 ms
    morinda>
    

    Use the information contained in this traceroute output to fill in the missing IP addresses in the "Internet Structure" diagram in the lecture.

12. (Thinking problem) The 32-bit IP address gives a huge address space, yet one of the big problems in Internet management is exhaustion of available IP addresses. Why is this so?