Subnet.

A contiguous range of IP addresses that share a common prefix, defining a single broadcast domain and routing boundary on a network. It belongs to the Network Security category of cybersecurity.

A contiguous range of IP addresses that share a common prefix, defining a single broadcast domain and routing boundary on a network.

A subnet (subnetwork) groups IP addresses that share the most significant bits of their address into a single layer-3 network. The split between network and host bits is given by a subnet mask or, in CIDR, a prefix length such as /24. Hosts in the same subnet communicate directly via ARP or IPv6 Neighbor Discovery; traffic to other subnets is forwarded through a router. Subnetting supports efficient address allocation, isolates broadcast traffic, and underpins network segmentation. In security architectures it forms the boundary for VLANs, ACLs, firewall rules, and microsegmentation. Misconfigured subnets - too large, overlapping, or routed across trust zones - are a recurring source of lateral-movement risk.

Defences for Subnet typically combine technical controls and operational practices, as detailed in the full definition above.

Common alternative names include: Subnetwork, IP subnet.