A Brief Introduction to IP Addresses
In the most widely installed level of the Internet Protocol (IP) today, an IP address is a 32-bit number that identifies each sender or receiver of information that is sent in packets across the Internet. The IP address is usually expressed as four decimal numbers, each representing eight bits, separated by periods. This is sometimes known as the dot address and, more technically, as dotted quad notation. For example, 127.0.0.1 could be an IP address. For a valid IP address all the four octets must have value between 0-255.
Beside decimal form, another important representation of an IP number is its binary form. For example, the address 192.168.73.245 represents the 32-bit binary number 11000000.10101000.1001001.11110101.
The binary number is important because that will determine which class of network the IP address belongs to. The Class of the address determines which part belongs to the network address and which part belongs to the node address. The location of the boundary between the network and host portions of an IP address is determined through the use of a subnet mask.
Further IP addresses can be assigned as Static(remains same) or Dynamic(may change each time you connect to the internet) by the Internet Service Providers (ISPs).
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IP Address Classes
The class of an address specified which of the bits were used to identify the network, the network ID, or which bits were used to identify the host ID, host computer. It also defined the total number of hosts subnets per network. There were five classes of IP addresses: classes A through E.
Class A IP Address
Class A allows for 126 networks by using the first octet for the network ID. The first bit in this octet, is always set and fixed to zero. And next seven bits in the octet is all set to one, which then complete network ID. The 24 bits in the remaining octets represent the hosts ID, allowing 126 networks and approximately 17 million hosts per network. Class A network number values begin at 1 and end at 127. Number 127.x.x.x is reserved for loopback, used for internal testing on the local machine.
Class B IP Address
Class B allows for 16,384 networks by using the first two octets for the network ID. The two bits in the first octet are always set and fixed to 1 0. The remaining 6 bits, together with the next octet, complete network ID. The 16 bits in the third and fourth octet represent host ID, allowing for approximately 65,000 hosts per network. Class B network ranges from 128.0.0.0 - 191.255.0.0.
Class C IP Address
Class C allows for approximately 2 million networks by using the first three octets for the network ID. In class C address three bits are always set and fixed to 1 1 0. And in the first three octets 21 bits complete the total network ID. The 8 bits of the last octet represent the host ID allowing for 254 hosts per one network. Class C network ranges from 192.0.0.0 - 223.255.255.0.
Class D IP Address
Class D addresses have their first three bits set to "1" and their fourth bit set to "0". Class D addresses are 32-bit network addresses, meaning that all the values within the range of 224.0.0.0 – 239.255.255.255 are used to uniquely identify multicast groups. There are no host addresses within the Class D address space, since all the hosts within a group share the group's IP address for receiver purposes.
Class E IP Address
Class E addresses are defined as experimental and are reserved for future testing purposes. They have never been documented or utilized in a standard way.
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