Subnetworking

Subnetworking, or subnetting, is the practice of dividing a larger IP network into smaller subnets. This division improves routing efficiency, reduces broadcast traffic within each subnet, and enables more precise address management and administrative control.

In IPv4, subnetting uses subnet masks to separate the network portion of an address from the host portion. CIDR notation shows this boundary, for example 192.168.1.0/24, where the /24 indicates the first 24 bits form the network address. Subnet masks define how many hosts can be addressed within each subnet. Techniques such as variable length subnet masking (VLSM) allow networks to use different subnet sizes as needed.

Subnetting supports hierarchical addressing and route aggregation, helping routers summarize routes and reduce routing table sizes. Routers connect different subnets and route traffic between them, while devices on a subnet share a common network segment. In many networks, subnetting is implemented together with VLANs, which separate broadcast domains at the link layer and are paired with distinct subnets at the network layer.

Historically, classful addressing imposed fixed boundaries, leading to inefficient address use. Subnetting and CIDR emerged to improve utilization and scalability. IPv6 uses a similar principle with fixed-length subnets defined by prefix lengths, typically allocating a /64 per subnet.

Benefits of subnetworking include improved performance, enhanced security through segmentation, and scalable growth. Successful subnet design requires careful address planning to avoid overlaps, ensure sufficient host capacity, and align with routing policies and security controls. Subnetting remains fundamental in enterprise networks, data centers, and service provider architectures.