Classless Inter-Domain Routing

CIDR notation is a quick way of writing a subnet mask that allows for advanced networking.

After the IP address put a slash followed by the number of network bits.

192.168.1.2 with a mask 255.255.224.0 = 11111111 .11111111 .11100000 .00000000

There are 19 contiguous 1's, so the CIDR notation is 192.168.1.2/19.

CIDR notation is a compact representation of an IP address and its associated routing prefix.