IPv4 subnet planner

VLSM Calculator

Split one network into subnets of different sizes. Enter the parent block and the hosts each subnet needs. Every block is sized to fit and placed on its boundary, largest first.

Parent network

Use /31 for 2-host linksPoint-to-point links per RFC 3021, with no network or broadcast address. Use /32 for single-address entriesLoopbacks and similar. Applies when a subnet needs exactly 1 host.

Subnet requirements

Usable hosts each subnet must hold. Enter moves to the next field. You can also paste a list, one subnet per line.

Each subnet gets the smallest block with room for its hosts plus the network and broadcast addresses: 2ⁿ − 2 ≥ hosts. Placing blocks in descending size order keeps every block aligned and leaves all free space in one run at the end of the parent network.