CIDR notation represents an IP address range using a combination of an IP address and its associated network mask. Instead of specifying the network mask in IP format (xxx.xxx.xxx.xxx), CIDR notation uses number.
The format of CIDR notation is:
Where xxx.xxx.xxx.xxx is the address space, and n is the number of left most 1 bits in the network mask.
For example, if 'n' is 18, then the corresponding network mask is: 255.255.3.0
There are online tool, which accepts input in CIDR format and outputs the IP range for example refer: http://www.ipaddressguide.com/cidr
Given below is a program I wrote in node.js, which produce the IP range for a given CIDR input: