3Com 3c17300 Implementation Guide - Page 89

IP Addresses 91 Dotted Decimal Notation The actual IP address is a 32-bit number that is stored in binary format. These 32 bits are segmented into 4 groups of 8 bits - each group is referred to as a field or an octet. Decimal notation converts the value of each field into a decimal number, and the fields are separated by dots. Figure 28 Dotted Decimal Notation for IP Addresses 10011110.01100101.00001010.00100000 = Binary notation 158.101.10.32 = Decimal notation The decimal value of an octet whose bits are all 1s is 255. Network Portion The location of the boundary between the network part and the host part depends on the class that the central agency assigns to your network. The three primary classes of IP addresses are as follows: ■ Class A address - Uses 8 bits for the network part and 24 bits for the host part. Although only a few Class A networks can be created, each can contain a very large number of hosts. ■ Class B address - Uses 16 bits for the network part and 16 bits for the host part. ■ Class C address - Uses 24 bits for the network part and 8 bits for the host part. Each Class C network can contain only 254 hosts, but many such networks can be created. The high-order bits of the network part of the address designate the IP network class. See Table 8. Table 8 How Address Class Corresponds to the Address Number Address Class A B C High-order Bits 0nnnnnnn 10nnnnnn 11nnnnnn Address Number (Decimal) 0-127 128-191 192-254