Dictionary.net

(Internet address) The 32-bit number uniquelyidentifying a node on a network using Internet Protocol,as defined in STD 5, RFC 791. An IP address is normallydisplayed in dotted decimal notation, e.g. 128.121.4.5.The address can be split into a network number (or networkaddress) and a host number unique to each host on thenetwork and sometimes also a subnet address.The way the address is split depends on its "class", A, B or C(but see also CIDR). The class is determined by the highaddress bits:Class A - high bit 0, 7-bit network number, 24-bit hostnumber. n1.a.a.a 0 <= n1 <= 127Class B - high 2 bits 10, 14-bit network number, 16-bit hostnumber. n1.n2.a.a 128 <= n1 <= 191Class C - high 3 bits 110, 21-bit network number, 8-bit hostnumber. n1.n2.n3.a 192 <= n1 <= 223DNS translates a node's fully qualified domain name to anInternet address which ARP (or constant mapping)translates to an Ethernet address.