Addressing schemes

Each IP address is made of two parts in such a way that the netid defines a network and the hostid identifies a host on that network. An IP address is usually written as four decimal integers separated by decimal points i.e. 239.247.135.93. If this IP address changes from decimal-point notation to binary form, it becomes 11101111 11110111 10000111 01011101. Thus, we see that each integer gives the value of one octet (byte) of the IP address. IP addresses are divided into five different classes: A, B, C, D and E. Classes A, B and C differ in the number of hosts allowed per network. Class D is used for multicasting and class E is reserved for future use. Table 2.3 shows the number of networks and hosts in five different IP address classes. Note that the binary numbers in brackets denote class prefixes. The relationship between IP address classes and dotted decimal numbers is summarised in Table 2.4, which shows the range of values for each class. The use of leading bits as class prefixes means that the class of a computer’s network can be determined by the numerical value of its address. A number of IP addresses have specific meanings. The address 0.0.0.0 is reserved and 224.0.0.0 is left unused. Addresses in the range 10.0.0.0 through to 10.255.255.255 are available for use in private intranets. Addresses in the range 240.0.0.0 through to 255.255.255.255 are class E addresses and are reserved for future use when new protocols are developed. Address 255.255.255.255 is the broadcast address,