Class A addresses range from 0.0.0.0 to 127.255.255.255. Class B ranges from 128.0.0.0 to 191.255.255.255 and class C from 192.0.0.0 to 223.255.255.255
A classless routing protocol includes the subnet mask in the routing update, Classful does not.
Classless routing protocols allow the use of VLSM and CIDR
If the network address in the routing update is on the same major classful network as the receiving interface, the classful routing protocol will use the same mask as the interface. Otherwise, it will use the default class mask.
CIDR and NAT helped with the problem with IPv4 addresses becoming depleted.
Subnetting a subnet is known as VLSM (Variable length subnet masking)
Supernetting refers to the ability to summarize networks less than the classful default mask. Classless routing protocols are required to propagate a supernet route because the subnet mask must be included with the summarized network address.
CIDR=Classless inter-domain routing
