IPv4 NETWORK PLANNING

VLSM Calculator

Allocate different subnet sizes based on the hosts each network needs.

Enter a prefix from /0 to /30. An IP with host bits set is normalized to its network address.

Subnet requirements

Hosts means usable addresses, including any gateway you need. Each subnet reserves one network and one broadcast address. Minimum allocation: /30 (2 usable hosts). /31 point-to-point links and /32 routes are not included.

How the VLSM calculation works

Variable Length Subnet Masking divides a parent network into subnets of different sizes. This calculator sorts your requirements from largest to smallest and assigns each subnet the smallest power-of-two block that fits its hosts plus the network and broadcast addresses.

For example, 50 hosts need a block of 64 addresses: a /26 subnet with 62 usable hosts. Unallocated addresses remain outside the assigned subnets; spare hosts are unused usable addresses inside them.