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VLSM Calculator

Allocate subnets of different sizes from one address block. Enter your base network and the number of hosts each subnet needs.

Subnet nameHosts needed

Related Tools

Subnet Calculator

Enter any IPv4 address and CIDR prefix or dotted subnet mask like 255.255.255.0. Network address, broadcast, host range, and wildcard mask calculate instantly. The built-in visual subnet calculator lets you split and rejoin blocks interactively.

CIDR Range Viewer

List every IP address in a subnet block. Enter a network address and CIDR prefix - usable hosts, network and broadcast addresses are highlighted.

VLAN Planner

Design your network segmentation - assign VLAN IDs, names, and subnets with live validation and CSV export.

About this tool

VLSM (Variable Length Subnet Masking) lets you divide a single IP block into subnets of different sizes, each sized exactly for its purpose. Subnets are allocated largest-first to minimise alignment waste - a /26 (62 hosts) must start at a multiple of 64, so allocating it first avoids losing addresses to boundary alignment.

Each row in the table shows the network address, subnet mask, the usable host range (first and last assignable IPs), and the broadcast address. "Wasted" addresses are those in the block above the hosts you requested - unavoidable overhead from power-of-two block sizes. The unallocated row shows the remaining contiguous address space.