lecture3:Subnetting

To overcome address depletion and give more organizations access to the Internet, classless addressing was designed and implemented. In this scheme, there are no classes, but the addresses are still granted in blocks.
Classless Inter-Domain Routing (CIDR) is an IP addressing scheme that was developed after the class system of A, B, C, D, and E [uses a slash followed by a number to highlight the network portion of an address instead of using a subnet mask].
The traditional class system considers an IP address as four octets with the network portion of the address highlighted by a subnet mask. The standard network portion is the first octet, the first two octets, or the first three octets. CIDR addressing still represents IP addresses in the traditional dotted decimal notation, but highlights the network portion with a slash followed by a number. For example:
192.168.3.15/26
172.21.165.1/19
The number after the slash is the number of bits that represent the network portion of the IP address. CIDR was developed to increase the efficiency of address allocation and to alleviate overloaded Internet routers.

Type of addressing in IPv4
Within the address range of each IPv4 network, we have three types of addresses:
Network address - The address by which we refer to the network
Broadcast address - A special address used to send data to all hosts in the network