How to use the IPv6 Subnet Calculator tool
- Enter an address like 2001:db8:abcd:12::1/64.
- Read the network, range and other values.
- Choose a longer prefix and click “List first subnets” to plan subnets.
How IPv6 prefixes work
IPv6 addresses have 128 bits, written as eight groups of four hexadecimal digits. Leading zeros in a group can be dropped, and one run of all-zero groups can be replaced with ::, which is why 2001:0db8:0000:0000:0000:0000:0000:0001 becomes 2001:db8::1. The calculator shows both forms following RFC 5952.
Subnetting in IPv6 is mostly about prefixes rather than host counts. A /64 is the standard size for a single LAN, because stateless address autoconfiguration (SLAAC) needs 64 bits for the interface identifier. Internet providers typically assign a /48 or /56 to a site, which gives 65,536 or 256 /64 networks.
Address types
- 2000::/3: global unicast, the public internet.
- fc00::/7: unique local addresses, the IPv6 equivalent of private ranges.
- fe80::/10: link-local, present on every interface and never routed.
- ff00::/8: multicast. IPv6 has no broadcast.
- 2001:db8::/32: reserved for documentation and examples.
Privacy
All calculations run in your browser. Nothing you enter is sent anywhere.
Frequently asked questions
Why is there no broadcast address in IPv6?
IPv6 replaced broadcast with multicast, so every address in a subnet can be used.
Should I use a /64 for every LAN?
Yes. Smaller subnets break SLAAC and some features. Use /127 for point-to-point router links.
How many /64 networks are in a /48?
65,536.
What is the ip6.arpa name used for?
Reverse DNS. It lists every hexadecimal digit of the address in reverse order.