About VLSM IP Plan Designer

Builds a variable-length subnet mask plan entirely in the browser. Requirements are sized and allocated largest-first to reduce fragmentation, while equal-sized entries preserve their original order. The result includes every subnet boundary, usable range, broadcast address, spare host capacity, overflow requirement, and remaining CIDR block.

• Standard mode reserves network and broadcast addresses and uses /30 as the smallest subnet.
• Optional edge-prefix mode treats /31 as a two-address point-to-point link and /32 as a single host route.
• Parent addresses with host bits are normalized visibly before allocation.
• No network names, addresses, requirements, or exported plans leave the browser.

Frequently Asked Questions

Why are networks allocated largest-first?

Larger blocks have stricter alignment requirements. Placing them first avoids gaps that can prevent a valid plan even when the parent network has enough addresses overall.

When should I allow /31 and /32?

Use /31 for point-to-point links where both addresses are endpoints, and /32 for host routes. Leave the option off for ordinary LAN subnets that reserve network and broadcast addresses.