Subnetting Explained: Dividing Networks with CIDR

An IP address is 32 bits long (IPv4). Without subnetting, the entire address space would be one flat network — unmanageable and insecure. Subnetting solves this by splitting a network into smaller segments called subnets. CIDR (Classless Inter-Domain Routing) notation expresses both the address and the subnet mask in one compact form. For example, 192.168.1.0/24 means the first 24 bits are the network portion, leaving 8 bits for hosts — that gives you 254 usable host addresses. A /25 splits that block in two: 192.168.1.0/25 (hosts .1–.126) and 192.168.1.128/25 (hosts .129–.254). Each subdivision doubles the number of subnets and halves the number of hosts per subnet. Subnetting is essential for routing efficiency, security isolation (putting servers on a separate subnet from workstations), and conserving IP space. With IPv4 exhaustion a reality, careful subnetting remains a critical skill for every network engineer.