IPv4 VLSM subnet planner
IPv4 VLSM calculator with full table, address space visualization, compare mode, step-by-step view, and CSV export to plan subnets without overlaps.
Plan IPv4 subnets with VLSM and avoid overlaps
IPv4 VLSM subnet planner with full table
Enter a base CIDR network, define required hosts, and generate a subnet plan with summary, detailed table, export, and address space visualization.
Complete the base network and required networks.
Address space
Tap a segment to highlight its subnet in the table or cards.
Subnet table
| Name | Network/CIDR | Mask | Wildcard | First host | Last host | Broadcast | Gateway | Required hosts | Usable hosts | Waste | |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Add requirements and generate the plan to see results. | |||||||||||
Copy configuration
Neutral format with fields NAME, NETWORK, CIDR, MASK, GATEWAY, FIRST_HOST, LAST_HOST, BROADCAST.
1) Base network
Define the base network in CIDR and review alignment warnings.
2) Required networks
Add your networks, specify hosts and required reserve.
3) Options
Choose the allocation strategy and suggested gateway.
4) Results
Review the table in card format and copy the configuration.
Scenario A
Options
Copy configuration A
Scenario B
Options
Copy configuration B
Comparison A vs B
| Scenario | Status | Subnets | Waste | Free |
|---|---|---|---|---|
| A | - | 0 | 0 | 0 |
| B | - | 0 | 0 | 0 |
How we calculate each subnet
Select a subnet to see the step by step. You can also show the first three for a quick review.
Generate a plan to see the step by step detail.
Frequently asked questions about the IPv4 VLSM planner
What is VLSM and what is it for?
VLSM (Variable Length Subnet Mask) lets you divide an IPv4 network into subnets of different sizes, adjusting the prefix to the actual number of hosts. It helps optimize IP usage and avoid waste.
How is each subnet size calculated?
Add the required hosts and reserve, include the network and broadcast overhead (when applicable), and round up to the next power of 2 to get the block size.
Why reserve IPs for network and broadcast?
In traditional IPv4 networks, the first IP in the block is the network address and the last is broadcast. That is why two usable IPs are subtracted in LAN blocks.
What is the wildcard and what is it used for?
The wildcard is the inverse mask (bits set to 1 where the subnet mask has 0). It is used in ACLs and configurations where ranges with flexible bits are specified.
What happens if the base network has no space?
The planner indicates which subnet does not fit and suggests expanding the base network, reducing reserves, or using the size strategy to improve the fit.
What is the difference between size and label strategies?
Size orders from largest to smallest and usually minimizes waste. Label respects the user order, but can leave less efficient gaps.
How is the gateway suggested?
You can choose whether the gateway is the first host, the last, or not suggested. The calculator applies it automatically in the table and the configuration block.
What are the current limitations?
The tool works with IPv4 and generates neutral text without vendor commands. The /31 option only applies when marked as P2P.
