subnetworks

Subnetwork, often shortened to subnet, is a logically defined subdivision of a larger computer network. It partitions a network into smaller pieces that share a common address prefix, enabling more efficient routing, better traffic management, and clearer policy enforcement. Subnetworks help limit broadcast domains and organize address space for administrative purposes, such as separating departments or security zones.

In IPv4 networks, subnets are defined by a subnet mask that separates the network portion of an address from the host portion. CIDR notation expresses this prefix length, for example 192.168.1.0/24. Routers route traffic between subnets, while switches and, in some cases, VLANs segment traffic at the data-link layer within a subnet. Subnetting enables hierarchical addressing, scalable routing, and more efficient use of available addresses. Network planners use techniques such as variable-length subnet masking (VLSM) to tailor prefix lengths to actual needs.

An example planning approach might subdivide 192.168.0.0/16 into multiple /24 subnets, such as 192.168.1.0/24 and 192.168.2.0/24, each supporting a defined number of hosts. Subnetting requires coordination of addressing, routing, and, where applicable, access control policies.

In IPv6, subnets are created by prefix lengths within a global prefix. Subnets commonly use a /64 prefix, with larger allocations for aggregate routing. IPv6 eliminates broadcast in favor of multicast-based techniques, but subnetting remains essential for scalable routing and network organization.