cidr vs subnet mask

 CIDR notation (Classless Inter-Domain Routing) is an alternate method of representing a subnet mask. It is simply a count of the number of network bits (bits that are set to 1) in the subnet mask. Subnet mask bits are explained in a following section. ... 0.0 (which has 8 network bits) would be represented as 131.10.

The term Subnetting is generally used when you use it at the organizational level. CIDR is generally used when you it at the ISP level or higher. In any event, it is only important to know that both terms really refer to the same concept. On local area networks, we use the concept of a subnet mask.

An IPv4 subnet mask consists of 32 bits; it is a sequence of ones (1) followed by a block of zeros (0). ... The following example shows the separation of the network prefix and the host identifier from an address (192.0.2.130) and its associated /24 subnet mask (255.255.255.0).

CIDR Available Networks (subnetting)

1. Subtract the network bits from 32. /17 = 32-17 and /21 = 32-21.
2. Raise 2 to that power. 232-17 and 232-21.
3. Divide the larger network by the smaller one. 232-17 / 232-21 = 215 / 211 = 215-11 = 24 = 16.