IP Address Classes

Source

This section looks at IP addressing, subnet masking, Private and Special addresses. Examples are provided to illustrate the methodology when setting up an IP network addressing scheme. We also look at Wildcard masks and Directed Broadcasts.

IP Address Classes

Unique IP (Internet Protocol) addresses are assigned to each physical connection of a device to a network, therefore if a device (host) has more than one connection to a network or networks, then it will have more than one IP address.

An IP address is represented as four decimal integers, with each integer corresponding to one byte this means an IP address is 32 bits long as per the following example:-

162.            146.            93.             14              dotted decimal
10100010.       10010010.       01011101.       00001110        binary

IP addresses are divided into two parts, a Network ID and a Host ID each of which can be of varying bit lengths but always making 32 bits altogether.

Hint:- Use the Windows calculator to convert binary to decimal and vice versa.

There are five primary classes of IP addresses and it is the high order 3 bits of the address which identify the class as shown below:-

First Octet         Example Network         Host
Class A 0xxxxxxx        1-127               25.234.45.0             1
Class B 10xxxxxx        128-191             140.250.43.0            1
Class C 110xxxxx        192-223             192.2.3.0               1
Class D 1110xxxx        224-239             232.56.4.0              1
Class E 11110000        240-254             242.5.7.0               1

Class A addresses contain 7 bits in the network portion giving 2⁷ - 2 = 126 possible networks since all 1's and all 0's are not allowed. Consequently 24 bits remain for the host portion allowing a total of 2²⁴ - 2 = 16,777,214 hosts. 127.0.0.0/8 is reserved for loopback address purposes where just 127.0.0.1 is used normally. The address 255.255.255.255 is used as broadcast addresses and 0.0.0.0 as a default route address, meaning any network. The address 0.0.0.0 is sometimes used by hosts that have yet to receive an IP address e.g. a DHCP Client awaiting an address from the DHCP server.

Class B addresses contain 14 bits in the network portion allowing 2¹⁴ - 2 = 16,384 possible networks, and 16 bits for the host portion allowing a possible total number of 2¹⁶ - 2 = 65,534 hosts.

Class C addresses contain 21 bits for the network portion giving a possible total of 2²¹ - 2 = 2,097,152 networks, and 8 bits for the host portion giving a possible 2⁸ - 2 = 254 hosts.

Class D addresses are used for multicasting and Class E addresses are used in research.

Historically, a company may have been allocated just one Class A, B or C IP address by the Network Information Centre (NIC). Currently, all Class A addresses have been allocated and most if not all of the Class B addresses have gone. If a company have a number of networks to manage then the network administrator may wish to subnet his network, that is create subnet addresses within the scope of the IP address that the administrator has been given.