CCNA Expl 2. Chapter 6.VLSM and CIDR

CCNA Exploration 2.Routing protocols and Concepts

RESUME. 

Chapter 6. VLSM and CIDR


Classful IP addressing.

Class	Start	End	network portion of the address	Hosts per network	Networks
Class A	0.0.0.0	127.255.255.255	8 bits	160777214	128
Class B	128.0.0.0	191.255.255.255	16 bits	65534	16384
Class C	192.0.0.0	223.255.255.255	24 bits	254	2097152
Multicast	224.0.0.0	239.255.255.255
Experimental	240.0.0.0	255.255.255.255

     
       RIPv1 summarizes subnets to a single major network classful address when sending the RIPv1 update out an interface that belongs to another major network.



In 1993, IETF introduced Classless Inter-Domain Routing, or CIDR (RFC 1517).
CIDR allowed for:
      ~  More efficient use of IPv4 address space
      ~  Prefix aggregation, which reduced the size of routing tables

        

      -   RIPv2, EIGRP, OSPF, IS-IS and BGP

The network portion of the address is determined by the network subnet mask, also known as the network prefix, or prefix length (/8, /19, etc.). 

       CIDR uses Variable Length Subnet Masks (VLSM) to allocate IP addresses to subnets according to individual need rather than by class.

        The ability for routes to be summarized as a single route helps reduce the size of Internet routing tables. 

        A supernet summarizes multiple network addresses with a mask less than the classful mask. 

        Classless routing protocols include the subnet mask with the network address in the routing update.

A supernet is always a route summary, but a route summary is not always a supernet.