INT21CN Computer Networks

Tutorial #12

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   203.12.120.56
   

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

4. What^[1] is the chief difference between the IP addressing scheme and the International (and Australian) telephone numbering scheme?

5. When a computer is being configured to connect to the Internet, in addition to setting its IP address the system administrator also usually configures an address mask or netmask parameter. Why is this needed? Is it likely to have a (sensible) default value?

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

7. The IP address 127.0.0.0 is reserved as the Internet loopback address. What do you think this means?

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. A certain company has 25 computers with full-time connections to the Internet. How many bits, of the 32 bits in the IP address, will be exactly the same in each of these computers, assuming they're allocated as a consecutive block? Is this a "maximum" value, a "minimum" value or an exact number? In the modern CIDR address allocation system, what would you expect to be the "/x" specifier at the end of the address block which is allocated to this company?