Understanding IPv4 Subnet Planning
An IPv4 network needs clear boundaries. The address identifies one device. The subnet mask defines the network part. The gateway sends traffic outside that network. This calculator connects those values. It returns the network address. It also returns the broadcast address. You also get the usable host range. The CIDR prefix appears beside the mask.
Why the Gateway Matters
A default gateway must be reachable locally. It should sit inside the same subnet. It should not use the network address. It should not use the broadcast address. Many networks place it first. Some networks place it last. This tool can suggest either value. It can also test a custom gateway.
Useful Planning Details
Subnet planning is about address capacity. A small prefix gives many hosts. A large prefix gives fewer hosts. The host requirement field helps with sizing. Enter the needed number of hosts. The calculator recommends the smallest common prefix. This prevents waste. It also reduces routing confusion. The output includes total addresses and usable hosts.
Reading the Results
The network address is the first address. It represents the whole subnet. The broadcast address is the last address. It reaches all hosts in that subnet. Usable addresses sit between them. The wildcard mask is the inverse mask. It is helpful in routing rules. It is also used in access lists. Binary rows show every bit. They help with learning and audits.
Best Use Cases
Use this page before assigning static addresses. Use it when checking router settings. Use it during lab work. Use it before firewall rule design. It can also support documentation. Export the report as CSV. Export the same result as PDF. Keep the file with your change notes. This gives a simple audit trail.
Accuracy Tips
Type every octet carefully. Each octet must be 0 through 255. Use a valid CIDR value. You may also enter a full mask. Avoid mixing old class rules with modern CIDR planning. Check the gateway status before saving settings. A correct gateway reduces connection errors.
Common Mistakes
Wrong masks create hidden outages. A gateway outside the subnet will fail. Duplicate gateway entries cause conflict. Save the calculated range. Then compare it with router and host settings.