WhenIP Academy
How to use WhenIP Subnet Calculator
The subnet calculator is useful whenever you need to confirm the network portion of an address, check a prefix, or verify a documentation value before using it in a firewall or route.
What you'll learn
- How to format IPv4 and IPv6 CIDR input.
- What the network and broadcast values mean.
- Why prefixes matter operationally.
Input format
Enter a CIDR such as 192.168.1.10/24 or 2001:db8::/64.
A slash prefix is required.
What you get back
For IPv4, WhenIP gives you at least the network and broadcast values.
For IPv6, the tool helps confirm the family and prefix context.
Why it helps
It is a fast way to sanity-check address plans, NAT rules, and security group entries.
Common mistakes
Leaving off the prefix, mixing IPv4 and IPv6 formatting, or assuming an address string is already the network address.
Mini FAQ
Can I paste a host IP instead of the network base?
Yes, as long as the CIDR prefix is included.
Why is there no broadcast in IPv6?
IPv6 does not use broadcast the same way IPv4 does.
Last updated: March 29, 2026