1-11 IP Addressing ConfigurationIP Addressing OverviewIP Address ClassesIP addressing uses a 32-bit address to identify each host on a network. An example is01010000100000001000000010000000 in binary. To make IP addresses in 32-bit form easier to read,they are written in dotted decimal notation, each being four octets in length, for example, 10.1.1.1 for theaddress just mentioned.Each IP address breaks down into two parts:z Net ID: The first several bits of the IP address defining a network, also known as class bits.z Host ID: Identifies a host on a network.For administration sake, IP addresses are divided into five classes, as shown in the following figure (inwhich the blue parts represent the address class).Figure 1-1 IP address classesTable 1-1 describes the address ranges of these five classes. Currently, the first three classes of IPaddresses are used in quantity.Table 1-1 IP address classes and rangesClass Address range DescriptionA 0.0.0.0 to 127.255.255.255Address 0.0.0.0 means this host nothis network. This address is used by ahost at bootstrap when it does notknow its IP address. This address isnever a valid destination address.Addresses starting with 127 arereserved for loopback test. Packetsdestined to these addresses areprocessed locally as input packetsrather than sent to the link.B 128.0.0.0 to 191.255.255.255 ––C 192.0.0.0 to 223.255.255.255 ––
