Each computer on a TCP/IP What is TCP/IP? based network (including the internet) has a unique, numeric address called an IP (Internet Protocol) address, enabling data packages to be addressed to this specific recipient.
An IP address consists of four so-called octets separated by dots. An octet is a binary number of eight digits, which equals the decimal numbers from 0 to 255. To make IP addresses easier to read and write, they are often expressed as four decimal numbers each separated by a dot. This format is called "dotted-decimal notation".
In a LAN based on TCP/IP, an IP address must be assigned to each host (computer or device) in the network. The IP address must be unique to each host.
Note: If two hosts were given the same address, the data to these hosts would be picked up randomly by one of them - be it the intended receiver or not - causing network irregularities.
Classes of IP Addresses:
In order to provide the flexibility required to support differently sized networks, IP addresses come in three classes - A, B, and C. Every class fixes the boundary between the network portion and the host portion of the IP address at a different point. This makes them appropriate for different size networks.
Class C addresses allow 254 hosts per network and are typically used by smaller and middle-sized companies. Class B networks a maximum of 16,384 hosts, while Class A networks allow more than 16 million hosts. As a consequence, Class A networks are only used by large organizations.
Calculating the number of possible hosts requires a closer look at the IP classes in their binary form. (The binary system is a base-2 number system, just like the base-10 number system is known as the decimal number system.) It is done as follows :
- in a Class C network, only the last octet is used to designate the hosts. the maximum decimal number that you can write using eight bits is 256 (28). The host calculation now requires that 2 is subtracted because two host addresses must be reserved for a network address and a broadcast address (for a further explanation of network and broadcast addresses, see the section on 'Subnets'). Ergo, the maximum number of hosts on a class C network is 256-2=254.
- A class B network allows a maximum of 16,384 hosts(216-2) per network (three octets are used to designate the hosts).
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