What is the chief advantage of CIDR over the original classful addressing scheme?
CIDR stands for Classless Inter-Domain Routing is a new addressing scheme for the Internet, that al lows for more efficient allocation of IP address than the old classful scheme.
Here a maximum number of networks and hosts which can be assigned using 32-bit classful addressing scheme. Several addresses are reserved for broadcasting and so on, and there were many wasted addresses also.
For illustration if you required 100 addresses you would be allocated the smallest class addresses (i.e. class C), but it still implies 154 unused addresses. Generally result was Interest was running out of unassigned addresses.
An associated problem was the size of the Internet global routing tables. When the number of networks on the Internet increased then did the number of route.
In place of being limited to network identifiers of 8 or 16 or may be 32 bits, CIDR currentty uses prefixes anywhere in between 13 to 27. Therefore, block of addresses can be assigned to networks as tiny as 32 hosts or to those with over to 5000,000 hosts. A CIDR address contains standard 32-bit IP address and also information that how many bits are used for the network prefix.
In the CIDR address 206.13.01.48/25, the 25 specify the first 25 bits are used to recognize the unique network leaving the remaining bits to recognize the exact hosts.
CIDR addressing scheme also allows route-aggregation wherein single high-level route entry can show many lower level routes into the global routing table.