Where the Subnet address is good a representing a standardized group of addresses that are subnets the IP Range type of address can describe a group of addresses while being specific and granular. It does this by specifying a continuous set of IP addresses between one specific IP address and another. While it is most common that this range is with a subnet it is not a requirement. For instance, 192.168.1.0/24 and 192.168.2.0/24 would be 2 separate subnets but if you wanted to descript the top half of one and the bottom half of the other you could describe the range of 192.168.1.128-192.168.2.127. It’s also a lot easier that trying to calculate the correct subnet mask.

The format would be:

There is a notation that is commonly used and accepted by some devices that follows the format:

This format is not recognized in FortiOS 5.2 as a valid IP Range.