While classful networks make life simpler, they are not efficient in terms of IP address usage. What if you want a Class C network with only two hosts on it? Well, for that network, you would need to have four IP addresses, that is, two for the hosts, one for the network address, and one for the broadcast address. We would have 252 IP addresses sitting there unused. Admittedly, that does give you scope to grow your network, but it is still not ideal.
CIDR provides us with the means of escaping from default subnet masks, thus allowing us to be more flexible in sizing our networks. Do you only want two hosts? Not a problem – we can create a subnet mask for that. CIDR is a key component in Variable Length Subnet Masks (VLSMs). VLSMs offer you the ability to break your network down into smaller networks of various sizes (as opposed to having multiple smaller...
