<P> IP networks may be divided into subnetworks in both IPv4 and IPv6 . For this purpose, an IP address is logically recognized as consisting of two parts: the network prefix and the host identifier, or interface identifier (IPv6). The subnet mask or the CIDR prefix determines how the IP address is divided into network and host parts . </P> <P> The term subnet mask is only used within IPv4 . Both IP versions however use the CIDR concept and notation . In this, the IP address is followed by a slash and the number (in decimal) of bits used for the network part, also called the routing prefix . For example, an IPv4 address and its subnet mask may be 192.0. 2.1 and 255.255. 255.0, respectively . The CIDR notation for the same IP address and subnet is 192.0. 2.1 / 24, because the first 24 bits of the IP address indicate the network and subnet . </P> <P> IP addresses are assigned to a host either dynamically at the time of booting, or permanently by fixed configuration of the host hardware or software . Persistent configuration is also known as using a static IP address . In contrast, when a computer's IP address is assigned newly each time it restarts, this is known as using a dynamic IP address . </P> <P> The configuration of a static IP address depends in detail on the software or hardware installed in the computer . Computers used for the network infrastructure, such as routers and mail servers, are typically configured with static addressing, Static addresses are also sometimes convenient for locating servers inside an enterprise . </P>

What are the numbers in an ip address called