Tools
VLSM Planner
Plan an IPv4 addressing scheme in seconds. Each subnet gets the smallest block that holds its hosts, the largest go first and nothing overlaps. If the plan will not fit, the planner tells you by how much instead of quietly dropping a subnet. Your plan never leaves your browser.
| Name | Hosts | Network | Mask | Host Range | Broadcast | Usable | Spare |
|---|
Spare space
How It Works
A subnet of prefix length p holds 232 − p addresses, two of which (the network and the broadcast) cannot be given to hosts. For each line we find the smallest block that still holds the hosts you asked for, sort the blocks largest first and lay them out from the start of the parent. Placing them in that order keeps every block on its own boundary with no gaps between them, so whatever is left at the end is one tidy run of spare space, shown as the fewest blocks that cover it.
Check a single subnet with the subnet calculator, or read the IPv4 design guide for how to leave room to grow.
Addressing more than one site, or inheriting a scheme nobody wrote down? Our network design reviews put a senior engineer on it with you, and you get back diagrams and an address plan your team can maintain.