Classless Inter-Domain Routing (CIDR) is an efficient method for allocating and routing IP addresses.
CIDR notation looks like an IP address, but ends with a slash and a number. Example: 192.168.0.0/24
The /24 refers to a netmask. In this case, /24 is 24 bits, or three bytes. Therefore, the first three octets are the network bits, and the last octet are the host bits. Performing a bitwise AND operation against the provided IP address “192.168.0.0” and “255.255.255.0” yields a netmask. If a netmask is ANDed by an IP address and the result equals the netmask, the IP address resides in the network:
192.168.0.0 = 11000000.10101000.00000000.00000000 <- same 255.255.255.0 = 11111111.11111111.11111111.00000000
AND operation = 11000000.10101000.00000000.00000000
192.168.1.0 = 11000000.10101000.00000001.00000000 255.255.255.0 = 11111111.11111111.11111111.00000000
AND operation = 11000000.10101000.00000001.00000000
192.168.0.2 = 11000000.10101000.00000000.00000010 255.255.255.0 = 11111111.11111111.11111111.00000000
AND operation = 11000000.10101000.00000000.00000000 <- same