Sub network

    IP networks can be divided into subnetworks in IPv4 and IPv6. For this purpose, the recognized IP address consists of two parts: the network prefix in the high-order bits and the remaining bits called the remainder field, the host identifier , or interface identifier (IPv6), is used for the numbering of hosts in the network. The subnet mask or CIDR notation determines how an IP address is divided into network and host parts.

    The term subnet mask is only used in IPv4. But both versions of IP use the CIDR concept and notation. In this case, the IP address is followed by a slash and the number (in decimal) of the bits used for the network portion, also called the routing prefix . For example, an IPv4 address and subnet mask could 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 an IP address indicate the network and subnet.