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Creating a subnet by dividing the host identifier
A subnetwork, or subnet, is a logically visible subdivision of an IP network. The practice of dividing a network into two or more networks is called subnetting. All computers that belong to a subnet are addressed with a common, identical, most-significant bit-group in their IP address. This results in the logical division of an IP address into two fields, a network or routing prefix and the rest field or host identifier. The rest field is an identifier for a specific host or network interface. The routing prefix is expressed in CIDR notation. It is written as the first address of a network, followed by a slash character (/), and ending with the bit-length of the prefix. For example, 192.168.1.0/24 is the prefix of the Internet Protocol Version 4 network starting at the given address, having 24 bits allocated for the network prefix, and the remaining 8 bits reserved for host addressing. The IPv6 address specification2001:db8::/32 is a large network with 296 addresses, having a 32-bit routing prefix. In IPv4 the routing prefix is also specified in the form of the subnet mask, which is expressed in quad-dotted decimal representation like an address. For example, 255.255.255.0 is the network mask for the 192.168.1.0/24 prefix. Traffic between subnetworks is exchanged or routed with special gateways called routers which constitute the logical or physical boundaries between the subnets. The benefits of subnetting vary with each deployment scenario. In the address allocation architecture of the Internet using Classless Inter-Domain Routing (CIDR) and in large organizations, it is necessary to allocate address space efficiently. It may also enhance routing efficiency, or have advantages in network management when subnetworks are administratively controlled by different entities in a larger organization. Subnets may be arranged logically in a hierarchical architecture, partitioning an organization's network address space into a tree-like routing structure. Contents [hide] * 1 Network addressing and routing * 2 IPv4 subnetting * 2.1 Determining the network prefix * 2.2 Subnetting * 2.3 Special addresses and subnets * 2.3.1 Subnet zero and the all-ones subnet * 2.4 Subnet and host counts * 3 IPv6 subnetting * 4 See also * 5 References * 6 Further reading * 7 External links| -------------------------------------------------
Network addressing and routing
Computers participating in a network such as the Internet each have at least one logical address. Usually this address is unique to each device and can either be configureddynamically from a network server, statically by an administrator, or automatically by stateless address autoconfiguration. An address fulfills the functions of identifying the host and locating it on the network. The most common network addressing architecture is Internet Protocol version 4 (IPv4), but its successor, IPv6, is in early deployment stages. An IPv4 address consists of 32 bits, for human readability written in a form consisting of four decimal octets separated by full stops(dots), called dot-decimal notation. An IPv6 address consists of 128 bits written in a hexadecimal notation and grouping 16 bits separated by colons. For the purpose of network management, an IP address is divided into two logical parts, the network prefix and the host identifier or rest field. All hosts on a subnetwork have the same network prefix. This routing prefix occupies the most-significant bits of the address. The number of bits allocated within a network to the internal routing prefix may vary between subnets, depending on the network architecture. The host part is a unique local identification and is either a host number on the local network or an interface identifier. This logical addressing structure permits the...