Its a little more complicated than that, but not much. Go to ask jeeves.com and type in what is a subnet. There is a really good tutorial there on basic subnetting, how to find the network ID of a IP address and host ID if it is subnet that is not a mulitple of 8 like 192.168.2.50/23 which has a subnet mask of 255.255.254.0. It also explains CISD which basically is how to use the subnet masks of different bit lengths like 23bits instead of normal 8,16,24 bit ones.