Routers constitute logical or physical borders between the subnets, and manage traffic between them. This addressing structure permits the selective routing of IP packets across multiple networks via special gateway computers, called routers, to a destination host if the network prefixes of origination and destination hosts differ, or sent directly to a target host on the local network if they are the same. The host identifier is a unique local identification and is either a host number on the local network or an interface identifier. The number of bits allocated within a network to the prefix may vary between subnets, depending on the network architecture. This prefix occupies the most-significant bits of the address.

All hosts on a subnet have the same network prefix. In both architectures, an IP address is divided into two logical parts, the network prefix and the host identifier. The most common network addressing architecture is Internet Protocol version 4 (IPv4), but its successor, IPv6, has been increasingly deployed since approximately 2006. Usually, this address is unique to each device and can either be configured automatically by a network service with the Dynamic Host Configuration Protocol (DHCP), manually by an administrator, or automatically by the operating system with stateless address autoconfiguration.Īn address fulfills the functions of identifying the host and locating it on the network in destination routing. Network addressing and routing The concept of subnetting the IPv4 address space 200.100.10.0/24, which contains 256 addresses, into two smaller address spaces, namely 200.100.10.0/25 and 200.100.10.128/25 with 128 addresses eachĬomputers participating in an IP network have at least one network address.

Subnets may be arranged logically in a hierarchical architecture, partitioning an organization's network address space into a tree-like routing structure, or other structures, such as meshes. Subnetting may also enhance routing efficiency, or have advantages in network management when subnets are administratively controlled by different entities in a larger organization. In the address allocation architecture of the Internet using CIDR and in large organizations, efficient allocation of address space is necessary. The benefits of subnetting an existing network vary with each deployment scenario. A router serves as a logical or physical boundary between the subnets. Traffic is exchanged between subnets through routers when the routing prefixes of the source address and the destination address differ. Subnet masks are also expressed in dot-decimal notation like an IP address. The IPv6 address specification 2001:db8:: / 32 is a large address block with 2 96 addresses, having a 32-bit routing prefix.įor IPv4, a network may also be characterized by its subnet mask or netmask, which is the bitmask that, when applied by a bitwise AND operation to any IP address in the network, yields the routing prefix. For example, 198.51.100.0 / 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 routing prefix may be expressed as the first address of a network, written in Classless Inter-Domain Routing (CIDR) notation, followed by a slash character ( /), and ending with the bit-length of the prefix. The rest field is an identifier for a specific host or network interface.

This results in the logical division of an IP address into two fields: the network number or routing prefix, and the rest field or host identifier. : 1, 16 The practice of dividing a network into two or more networks is called subnetting.Ĭomputers that belong to the same subnet are addressed with an identical group of its most-significant bits of their IP addresses. Creating a subnet by dividing the host identifierĪ subnetwork or subnet is a logical subdivision of an IP network. For subnets in the mathematics of topology, see Subnet (mathematics).

Ip subnet mask