NA Lesson - 12

CIDR Concepts

 Session Objectives :

·                     Concept of CIDR

·                     Examples of CIDR

CIDR

Classes in the domain routing as CIDR is commonly used to refer to supernetting in general.

           

It is an efficient method accounting for supernets within routing tables.

CIDR allows the entire supernet to be handled with a single entry as in the following fig.

• CIDR requires that routers use classless routing protocols such as RIP version 2 or the Open Shortest Path First (OSPF) routing protocol.
• Blocks of supernetted addresses assigned by Internet regional registries or by ISPs are often called CIDR blocks.
• CIDR is not compatible with Routing Information Protocol (RIP) version 1, a legacy protocol used in some older routers.

Address Space Perspective

• The use of CIDR to allocate addresses promotes a new perspective on IP network IDs.
•  In the preceding example, the CIDR block (131.107.0.0, 255.255.248.0) can be thought of in two ways:

            ■  A block of 8 Class C network IDs

            ■  An address space in which 21 bits are fixed and 11 bits are assignable.

•  In the latter perspective, network IDs lose their class-based heritage and become part of a classless IP address space. Each network ID, regardless of length, is an address space in which the network ID bits are fixed and the host bits are variable.
• The host bits are assignable as host IDs, or, using subnetting techniques, can be used in whatever manner best suits the needs of the organization.

 SN : General Network-wide means A class,B class,C class,IP adresses.