Visualize IP addresses and subnet masks for a Cisco Networking class. You enter an IP number and subnet mask. Netnums displays them in decimal, hex, and binary, determines the class of the network, and calculates how many subnets and hosts you can have. Netnums is aware that the first and last host address in each subnet are reserved for network and broadcast addresses respectively and that the entire first and last subnets are also restricted though they may be used in some cases.