Range of Addresses
You must set one or more ranges of addresses that define each OSPF area. A maximum of eight ranges can be set for each area. The address consists of the IP prefix shared by all IP addresses within the range and a netmask in the format <IP prefix/netmask>.
The netmask indicates the number of high-order bits within an address that must match those in the prefix for the address to belong within the area.
The netmask value is a number from 1 to 30, preceded by a slash (/)---for example 192.168.1.0/24.