IP Subnet Calculator

IP subnetting divides a network into smaller segments (subnets) for better organization, security, and performance. CIDR (Classless Inter-Domain Routing) notation expresses subnets as an IP address followed by a prefix length: 192.168.1.0/24 means the first 24 bits (three octets) identify the network and the remaining 8 bits identify hosts within that network. A /24 subnet has 256 addresses (254 usable hosts, minus network and broadcast addresses). Smaller prefix lengths create larger networks: /16 has 65,536 addresses, /8 has 16.7 million. Larger prefix lengths create smaller networks: /28 has 16 addresses (14 usable), /30 has 4 addresses (2 usable, commonly used for point-to-point links). The subnet mask is the binary representation of the prefix: /24 = 255.255.255.0, /16 = 255.255.0.0, /28 = 255.255.255.240. The AllTools IP Subnet Calculator takes a CIDR notation input and calculates: network address, broadcast address, first and last usable host addresses, total host count, subnet mask in dotted decimal, wildcard mask (inverse of subnet mask, used in ACLs), and binary representation. All calculations run locally in the browser using pure JavaScript arithmetic.

Subnet planning is essential for designing network architectures in cloud, corporate, and data center environments. AWS VPC design requires planning subnets for public-facing resources (web servers, load balancers), private resources (application servers, databases), and isolated resources (management, monitoring). A typical VPC uses /16 for the VPC CIDR, with /24 subnets for each availability zone and tier. Azure Virtual Networks, Google Cloud VPCs, and private data center networks follow similar patterns. Security segmentation isolates sensitive systems into separate subnets with firewall rules controlling inter-subnet traffic — database servers in one subnet, application servers in another, and DMZ services in a third. Kubernetes pod networks use large subnets (/16 or larger) to accommodate thousands of pod IP addresses, with service networks on a separate CIDR range. Home network segmentation separates IoT devices from personal computers and guest networks. The AllTools calculator helps plan these architectures by showing exactly how many hosts each subnet size supports, what address ranges are available, and how subnets can be divided without overlap — all calculated locally without exposing your network architecture to external services.