CIDR is the short for Classless Inter-Domain Routing, an IP addressing scheme that replaces the older system based on classes A, B, and C. A single IP address can be used to designate many unique IP addresses with CIDR.
Here you can specify any CIDR range and it return the First and last IP.
https://www.ipaddressguide.com/cidr
https://build5nines.com/ipv4-address-cidr-range-reference-and-calculator/
Found above links quite useful to whitelist a range of IPs in Oracle Cloud Infrastructure or to find if an IP falls within a specific CIDR block