subnetz

Subnet

In short: A logically delimited part of a larger network that uses its own address ranges in order to structure networks and limit broadcast traffic.

In more detail: Subnets are created by dividing an address space with the help of a subnet mask, which determines which part of an IP address describes the network and which the specific device. Useful, for example, for separating a company’s departments (VLAN) or locations in network terms.

In Depth

Subnetting solves a real historical problem: the original IPv4 address space was divided into fixed classes (A, B, C), each with very large or very small network sizes — a company with 300 devices would have needed either a class C network that was far too small (254 usable addresses) or a class B network that was far too large (65,534 addresses, almost all of them wasted). Subnetting allows a larger address block to be divided flexibly into subnetworks of exactly the right size, instead of being bound to rigid class boundaries.

An example: 192.168.1.0/24 describes a network with 254 usable host addresses. If you split it by subnetting into four /26 subnets (192.168.1.0/26, .64/26, .128/26, .192/26), you get four separate network segments with 62 usable addresses each — e.g. one per department. Each subnet forms its own broadcast domain: broadcast traffic from one subnet doesn’t automatically reach the others, only via a router that explicitly forwards between the subnets.

See also: Subnet mask, VLAN, Network segment