VLSM Planner

VLSM (variable length subnet masking) splits one parent network into subnets of different sizes, so a 50-host VLAN and a 10-host VLAN don't both burn a /24.

For each line, the planner adds 2 to the host count (every IPv4 subnet loses its network and broadcast address), then rounds up to the next power of two. 50 hosts need 52 addresses, which rounds up to 64, a /26.

Requests are placed largest first. Each block starts on a boundary that is a multiple of its own size, so placing big blocks first keeps the small ones packed behind them with no gaps. If the total doesn't fit in the parent network, the planner says so instead of overlapping subnets.

The default plan splits 10.0.0.0/24 (256 addresses) into four networks:

Swipe the table sideways to see all columns ->

That uses 144 addresses and leaves 10.0.0.144 to 10.0.0.255 (112 addresses) free for later.

Yes. The planner sizes each subnet to the count you enter, so enter the count you expect in a few years, not today. Resizing a subnet later means renumbering devices.

The first address names the network and the last is the broadcast address, so neither can go to a device. Remember that your gateway also takes one of the usable addresses.

No. Every request gets at least a /30 (2 usable hosts). Point-to-point /31 links are allowed by RFC 3021 but are left out here to keep plans simple.