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IP Subnet Calculator

Calculate IPv4 or IPv6 subnet details including network address, host range, broadcast, subnet and wildcard masks, CIDR, reverse DNS and possible sibling networks.

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IP Subnet Calculator

Local calculation

Choose the IPv4 subnet mask from the dropdown. If the address already includes a CIDR suffix, that prefix takes priority. For IPv6, enter the prefix with the address, for example 2001:db8::1/64.

HOW IT WORKS

About the IP Subnet Calculator

The calculator performs the subnet arithmetic locally on the 39D server. For IPv4 it derives the network and broadcast addresses by applying the subnet mask, then calculates the usable host range, wildcard mask and identity formats. For IPv6 it applies the selected prefix length to calculate the network and final address; IPv6 has no broadcast address.

How to use this result

  1. Enter the IP address.Use an IPv4 or IPv6 address, optionally with its CIDR suffix.
  2. Choose the subnet.For IPv4 select the dotted subnet mask and CIDR prefix from the dropdown. For IPv6 include the prefix with the address, such as 2001:db8::1/64.
  3. Review the calculated network.The result shows the network boundary, usable range or address range, masks, totals and address representations.
  4. Review sibling subnets.The calculator lists every same-size subnet inside the nearest containing octet boundary for IPv4 or nibble boundary for IPv6.

Common interpretation issues

  • Class A, B and C labels are historical and modern routing uses CIDR, but the class is included for reference.
  • IPv4 /31 networks are commonly used for point-to-point links and use both addresses rather than reserving network and broadcast host addresses.
  • IPv6 does not reserve a broadcast address and normally uses multicast instead.

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Frequently asked questions

How do I choose the IPv4 subnet?

Use the subnet dropdown. Each option shows both the dotted-decimal subnet mask and its CIDR prefix, for example 255.255.255.240 /28.

Can I paste an address with the prefix already attached?

Yes. For example, 91.204.246.39/28 or 2001:db8::1/64. The attached prefix takes priority over the separate mask field.

Why is there an IP class when CIDR is used?

Classful A, B and C addressing is obsolete for modern routing, but it is still useful as a historical reference and is included in the detailed IPv4 output.