By ToolzHive
About this tool
The IPv6 subnet calculator works with 128-bit addresses exactly. Enter an address and prefix length to see the network prefix, the first and last addresses, the number of addresses and /64 subnets, the address type (global, link-local, unique local and more), the fully expanded and compressed forms and the reverse DNS name. You can also split a prefix, such as a /48, into /56 or /64 subnets.
How to use IPv6 Subnet Calculator
- Enter an IPv6 address, optionally with a prefix like 2001:db8::/48.
- Adjust the prefix length if needed.
- Read the network details and choose a size to divide it into subnets.
Worked example
An ISP assigns you 2001:db8:abcd::/48. That contains 65,536 /64 subnets, one for each LAN or VLAN, starting with 2001:db8:abcd::/64 and 2001:db8:abcd:1::/64.
Why is /64 the standard subnet size?
IPv6 address autoconfiguration (SLAAC) needs 64 bits for the interface identifier, so LANs almost always use /64 subnets.
How are IPv6 addresses compressed?
Leading zeros in each group are dropped, and one run of all-zero groups is replaced by ::. So 2001:0db8:0000:0000:0000:0000:0000:0001 becomes 2001:db8::1.
What is a unique local address?
Addresses starting with fc or fd (fc00::/7) are private, like 192.168.x.x in IPv4, and are not routed on the internet.
Put this guide into practice
- IPv6 Subnet Calculator — Calculate IPv6 prefixes, address ranges and subnets, and expand or compress addresses.