CIDR (Classless Inter-Domain Routing) notation is a compact method for specifying IP addresses and their routing suffixes. For example, we can express the idea that the IP address 192.168.0.1 is associated with the netmask 255.255.255.0 by using the CIDR notation of 192.168.0.0/24, where 24 represents the number of network bits in the IP address (IPv4 address has 32 bits, so the network can be between 0 and 32).