CIDR or Classless Inter-Domain Routing another IP addressing system that allows more flexible allocation of IP addresses compared to the original Classful addressing scheme (A, B, C, D and E). The Classful IP addressing scheme can be wasteful. For example, giving the minimum IP address allocation of 256 (Class C) to a network which only requires 15 addresses.
The table below shows us how many available addresses are there in subnet for a specific CIDR notation.
- 2(32-CIDR)= number of devices on the local network
- Number of valid host is always two less than the subnet block