Computer Networks

Tutorial #8

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. An IP address with all zeros in the host part is said to be a network address, and is not available to be allocated to any host on the network. What does this mean? Give an example of a Class B network address.

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

4. Calculate exactly how many hosts each of the three classes of IP address (class A, B & C) can support. Remember that some addresses are reserved for special purposes.

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

6. Why was it necessary to introduce subnetting into the IP address structure?

7. In modern subnet mask terminology the IP address of ironbark would be written as 149.144.21.60/24. How should this be interpreted?

8. In the lecture, it was stated that the broadcast address is an IP address with all 1's in the host part of the address. However, many systems in practice use a broadcast address format whereby all of the bits are 1, ie 255.255.255.255. How should this address be interpreted? Optional harder question: a broadcast address of the form discussed in the lecture is sometimes called a directed broadcast address. What do you think this means?^[2]

9. 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?

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?

11. Optional Practical Exercise: write^[1] a computer program that can translate between 32-bit numbers and dotted decimal form. Extend your program to determine whether the address is class A, B or C, and print the network and host portions. Further extend your program to recognise and identify special IP addresses such as the limited broadcast address, a directed broadcast address, etc.