Why not there is classful interdomain routing?

Question

Mostly we mention cidr as classless interdomain routing, so I thought of why not there is classful interdomain routing

I want to know what problems are there in classful addressing for interdomain routing

Note:
CIDR: stands for classless inter-domain routing
Interdomain Routing: means exchanging information between different networks that are under different administrative control eg. one controlled by IIT and another controlled by (say) AIIMS

Normally this mechanism uses classless addressing of IPv4 so named cidr

Protocol is BGP-Border Gateway Protocol which is a Exterior Gateway Protocol

My doubt is whether this mechanism is possible using classful addressing of IPv4 or if not why it is not possible?

Comments

Could not understand the doubt, can you rephrase the question i.e. which Protocol, what is the existing behavior and what is your doubt.

Answer 1

Classful addressing divides the address space for IPv4 into five address classes. Each class, coded in the first four bits of the address, defines either a different network size, i.e. number of hosts for unicast addresses (classes A, B, C), or a multicast network (class D). The fifth class (E) address is now IPv6.

Class           Leading bits    Size of network number bit field    Size of rest bit field  Number of networks  
Class A                0        8               24                       128                16,777,216 
Class B               10        16              16                     16,384               65,536 
Class C              110        24               8                  2,097,152               256
Class D (multicast) 1110        not defined     not defined       not defined               not defined  
Class E (reserved)  1111        not defined     not defined       not defined               not defined 

The above approach was fine however the problem was quick exhaust of the IPv4 address which was a precious resources and in 1993 IETF published the new RFCs 1518 and 1519 which describes the new way of allocation of IP address and routing method of the IP packet.

http://tools.ietf.org/html/rfc1518
http://tools.ietf.org/html/rfc1519

Comments

thank you sir