CIDRCIDR stands for Classless Inter- Domain Routing, notation, which has replaced the old classful-address+netmask notation since 1993. In CIDR notation, the I.P. address is followed by a solidus ('/') and one or two decimal digits. These digits specify how many bits of the I.P. address are used to determine the network address, with the remaining bits being used to determine the host address on the given network. For example, an old-style Class C address, which would have had a netmask of 255.255.255.0, is now referred to as a /24 (pronounced "slash twenty-four") address. For more information, please see Wikipedia's CIDR page.