When designing networks or coming up with firewall rules, sometimes it's handy to have a subnet calculator around. This tool helps you figure out netmasks and how many hosts can fit into a subnet.
To use this tool, just put in an IPv4 or IPv6 address and subnet mask (in CIDR notation).
For IPv4 networks, the calculator will return:
- IP
- Netmask
- Wildcard mask (the inverse of the net mask)
- CIDR notation
- Network address
- Usable range
- Broadcast address
- Number of usable hosts
For IPv6 networks, the calculator will return:
- Expanded notation
- Condensed notation
- CIDR notation
- Usable range
- Number of usable hosts
When to use a subnet calculator
- Designing a network or adding new equipment - Use the tool to help you figure out how to divide the networks and integrate new and existing network equipment.
- For practice! - If you're practicing for an exam, you can use the calculator to make sure your subnet calculations are correct.
- Creating/validating firewall rules - Firewalls often take in CIDR notation. CIDR notation is nice shorthand for describing a block of addresses, but isn't always the most intuitive. You can use the calculator to verify that the hosts you are allowing fall within the usable range.