IPv6 subnet calculator
Expand, compress, and subnet any IPv6 prefix. See the network address, the first and last address, the block size, and the address type, instantly in your browser.
Supports :: compression and embedded IPv4. Documentation prefix 2001:db8::/32 is safe to experiment with.
Subnetting in IPv6 is about prefixes, not host counts
IPv6 has so many addresses that counting hosts stops being useful. A single /64, the normal LAN size, holds more addresses than the entire IPv4 internet squared. So IPv6 subnetting is about carving prefixes: a provider hands you a /48, you split it into 65,536 /64s, and each /64 becomes one subnet.
This calculator handles the parts that trip people up: expanding the shorthand :: back to all eight groups, compressing a full address down again, and finding the network boundary for a given prefix. It recognises common types too, from link-local fe80::/10 to unique-local fc00::/7. For IPv4 work, switch to the subnet calculator.
Frequently asked questions
How big is an IPv6 subnet?
Enormous. A /64, the standard LAN size, holds 18 quintillion addresses. Because the numbers are astronomical, this calculator shows the count as a big integer rather than a host list.
Why is /64 the standard IPv6 subnet?
IPv6 stateless address autoconfiguration (SLAAC) expects a 64-bit interface identifier, so a /64 is the smallest subnet that works normally on a LAN. Provider allocations are typically /48 or /56.
What does :: mean in an IPv6 address?
The double colon compresses one run of all-zero groups. 2001:db8:0:0:0:0:0:1 becomes 2001:db8::1. It can appear only once in an address. This tool expands and compresses both ways.
What is 2001:db8::/32?
It is the documentation prefix reserved for examples and manuals, the IPv6 equivalent of 192.0.2.0/24. It is safe to use in guides and test configs because it is never routed on the public internet.