Undernät

Undernät is a Swedish term that translates to “subnetwork” in English. It refers to an administrative division of a larger computer network that is logically isolated from the rest of the network but shares the same physical infrastructure. By partitioning the overall network into smaller segments, undernät support better traffic management, policy enforcement, and security control.

The primary purpose of an undernät is to organise IP address space in a scalable and efficient way. In practice, an undernät is defined by an IP address block and a subnet mask, typically expressed using Classless Inter-Domain Routing (CIDR) notation. For example, the block 192.168.10.0/24 represents an undernät with 256 addresses, of which 254 are usable for hosts. Python-like notation makes it straightforward to allocate distinct address ranges to departments, servers, or device types and to minimise address wastage.

Beyond address allocation, undernät enable the use of virtual LANs (VLANs) to further segment traffic at the Ethernet frame level. VLAN tagging lets a single physical switch appear as multiple logical switches, letting administrators apply access control lists, Quality of Service policies, and traffic isolation with minimal hardware changes. DHCP scopes and security appliances are commonly scoped to individual undernät, allowing fine‑grained control over network services.

In enterprise and service‑provider environments, undernät assist with routing and redundancy. Each undernät can be routed via dedicated routing protocols such as OSPF or BGP, and can be protected with redundant links or virtual routers. The result is a modular network architecture that can accommodate growth, isolate faults, and simplify troubleshooting.

Simple concepts, such as subnetting, IP allocation, and VLAN tagging, make undernät a foundational tool for modern network design, enabling robust, flexible, and secure communication infrastructures.