IPv4 Subnet Builder - Online Visual Range Calculator

An IPv4 subnet is a logical subdivision of an IP network. It allows you to divide a larger network into smaller, manageable segments, improving efficiency and security. Subnets are defined by a network address and a subnet mask (or CIDR prefix).

A subnet mask is a 32-bit number that masks an IP address to identify the network portion and the host portion. It is typically written in dotted decimal notation (e.g., 255.255.255.0) or as a CIDR prefix length (e.g., /24). All bits set to 1 in the mask represent the network part, and 0s represent the host part.

CIDR (Classless Inter-Domain Routing) notation uses a slash followed by a number (e.g., /24) to indicate the number of bits used for the network prefix. It replaces the older classful network design and allows more flexible subnetting.

The number of usable hosts is 2^{(32 - prefix)} - 2. The subtraction accounts for the network address and the broadcast address, which cannot be assigned to devices. For example, a /24 network has 2⁸ - 2 = 254 usable hosts.

Private IP addresses are reserved for internal use within a local network and are not routable on the internet. The ranges are: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. This tool is perfect for planning subnet allocations within these ranges.

Subnetting improves network security, reduces congestion, and simplifies management. It allows you to isolate groups of devices, apply different policies, and make efficient use of limited IPv4 address space.

The broadcast address is the last address in a subnet, used to send data to all devices on that network simultaneously. It is calculated by setting all host bits to 1. For a network 192.168.1.0/24, the broadcast address is 192.168.1.255.

It provides an intuitive color-coded bar showing how your parent network space is divided among subnets. You can instantly see used and free areas, detect fragmentation, and avoid overlapping allocations — something traditional subnet calculators don't offer.

Yes. This tool is designed exactly for that. Define a parent network, then add as many subnets as you need. The auto-assign feature finds the best free space for each subnet based on host requirements, preventing overlaps.

You provide the number of required hosts; the tool computes the smallest possible subnet prefix that accommodates them. Then it searches for a free contiguous block within the parent network, using a best-fit algorithm to minimize wasted space, and creates the subnet automatically.