Computer Networks

Tutorial #7

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

   205.184.10.20	139.130.17.42	48.55.190.88
   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[1] is the chief difference between the IP addressing scheme and the International (and Australian) telephone numbering scheme?

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

4. 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?

5. We have seen that the address with all 1's in the host part is used as the IP broadcast address. What do you think the address with all 0's in the host part is used for?

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

7. Consider[2] 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.

8. Is[3] it possible to address a datagram to a router's (IP gateway's) IP address? Does it make sense to do so?

9. The following are the outputs of two old runs of the traceroute command, one looking from Bendigo towards the rest of the lnternet via La Trobe, Bundoora, and the other from outside La Trobe looking towards Bendigo. Note that the traceroute output given in the lecture shows an up-to-date representation of the structure of the Internet in the region of La Trobe University.

   12 ltu.gw.au ( 139.130.8.2) 252 ms 273 ms 123 ms
   13 149.144.1.2 (149.144.1.2) 398 ms 149 ms 273 ms
   14 r-itsbgo.bendigo.latrobe.edu.au (149.144.2.254) 531 ms * 408 ms
   15 busfddi0.bendigo.latrobe.edu.au (149.144.10.1) 244 ms * 273 ms
   16 ironbark (149.144.20.60) 316 ms 279 ms 480 ms
   
   1 149.144.20.254(149.144.20.254) 3ms 3ms 3ms
   2 itsfddi0.bendigo.latrobe.edu.au (149.144.10.254) 3 ms 4 ms 5 ms
   3 r-bgowan.bendigo.latrobe.edu.au (149.144.2.1) 6 ms 4 ms 10 ms
   4 Itu.gw.au 149.144.1.1 (149.144.1.1) 36 ms 32 ms 32 ms
   5 national.gw.au(139.130.8.1) 269ms 304ms 297ms
   

   1. Can you see where the large delays occur in datagram delivery?
   2. Use this information to draw a diagram of the topology of the Internet in our region at the time these traceroutes were run. You should show IP addresses of the various interfaces involved, and possibly network and subnet numbers (although these may only be a guess, since we don't know the subnet masks which are in use).
   3. How has the structure of the 'net changed since this traceroute was run?

10. (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?