What wildcard masks are, and how to use them in a Cisco IOS access list. For help calculating IP address summarizations, see the online CIDR/VLSM supernetting calculator. About the author: ...

For example, if there is a class C IP, its Subnet Mask would be 255.255.255.0 and the Subnet Prefix Lenght would be 24 as there are 24 network bits.