IP Addresses The Class System

Network Addresses An IP address is structured as four decimal numbers joined by dots. Each decimal number is coded as an octet (8 bits) e.g. 148.78.250.12 Figure 15.9 An IP address is stored in four bytes

Network Addresses An IP address can be split into network address, which specifies a specific network host number, which specifies a particular machine in that network There are 3 classes of address according to how much of the address is dedicated to each role.

Classes of Network Addresses To determine the class of an address, look at the first octet of the dotted-decimal address.        

Classes of Network Addresses Class A Octet 1: decimal value 1-126 (e.g. 10.1.23.19) In a class A address, the first octet is the network portion, so the class A example above has a major network address of 10. Octets 2, 3, and 4 are for the network manager to divide into subnets and hosts as she sees fit. Class A addresses are used for networks that have as many as 16,581,375 hosts.

Classes of Network Addresses Class B Octet 1: decimal value 128-191 (e.g. 172.16.19.48) In a class B address, the first two octets are the network portion, so the class B example above has a major network address of 172.16 Octets 3 and 4 (16 bits) are for local subnets and hosts. Class B addresses are used for networks that have between 256 and 65,536 hosts.

Classes of Network Addresses Class C Octet 1: 192-223 (e.g. 193.18.9.10) In a class C address, the first three octets are the network portion. The class C example above has a major network address of 193.18.9. Octet 4 (8 bits) is for local subnets and hosts - perfect for networks with less than 256 hosts.

Classes of Network Addresses What class are York’s IP addresses? Here’s a sample: 130.63.236.200