Abbreviation for classless inter-domain routing. A method that allows defining subnet masks without the constraint of using 8-bit boundaries that is normally created by classful networks. It uses variable-length subnet masking (VLSM). In CIDR notation, an IPv4 address is written by using the format <IP address/suffix> where suffix is the number of bits set to 1, starting from the left, when the mask is written in binary format and that represent the network ID portion of the IP address. For example, in 192.168.10.1/26, 26 corresponds to 11111111.11111111.11111111.11000000 in binary, which is subnet mask 255.255.255.192. The remaining 6 bits are used for IP addresses of the subnet (63 in this example, from 192.168.10.1 to 192.168.10.63).