ABSTRACT

Internet is made of a combination of Networks connected by Routers or Gateways. When a Source communicates with Destination, the packets may travel from one physical Network to another through Routers and Gateways. Therefore we need identification system to identify the source and destination. This can be done with a IP Address in TCP/IP Networks. An IP Address is a 32 bit binary address implemented in software that uniquely and universally defines Host or Router on the Internet.

IP Addresses are unique in the sense that two hosts in the Internet can never have the same Address, but a device can have more than one IP Address. Each IP Adress consists of 4 Octets each with 8 bits consisting Network ID and Host ID.
To cover the needs of different types of Organizations, IP Addresses are divided into 5 different Classes, Class A, Class B, Class C, Class D, Class E.

The existing classes of IP addressing system is not flexible , not secure and causes wastage of so many addresses. So it requires so may extensions, they are¦.
1. Subnetting
2. Supernetting or CIDR( Classless Inter Domain Routing )
3. Public and private hosts.

Subnetting:- In subnetting, a network is divided into smaller subnets with each sunet having its own subnet address. Reasons for subnetting includes broadcast problem, most IP Address assignments were not very efficiently, etc. In IPv4networks, the routing prefix is often expressed as a subnet mask, which is a bit mask covering the number of bits used in the prefix. An IPv4 subnet mask is frequently expressed in quad-dotted decimal representation, e.g., 255.255.255.0 is the subnet mask for the 192.168.1.0 network with a 24-bit routing prefix (192.168.1.0/24)

Supernetting:-(classless addressing) allows the addresses assigned to an organization to span multiple IP network addresses. Classless Inter-Domain Routing - collapse a block of contiguous network addresses into a single pair to keep routing tables short. Example: An organization wants to connect to the Internet, The organization would prefer a class B address, Plans to subnet its various physical networks using the third octet of the IP address to represent the subnet, This would allow the organization to have 254 physical networks with up to 254 hosts per network which is very difficult. This can be overcame by supernetting. Instead of getting a class B address, the organization is given 256 contiguous class C addresses, The organization can have up to 256 physical networks