IPv6 Subnet Calculator
Enter an IPv6 address and prefix length to find its network, address range and child-subnet count. IPv6 address counts do not predict how many devices you can practically assign.
Result
| Network | 2001:db8:1234:5678::/64 |
|---|---|
| Full network address | 2001:0db8:1234:5678:0000:0000:0000:0000 |
| Last address | 2001:db8:1234:5678:ffff:ffff:ffff:ffff |
| Address count | 18446744073709551616 |
| Host bits | 64 |
| Number of /64 subnets | 1 |
Note: IPv6 has no broadcast address. The all-zeros host address is the subnet-router anycast address (RFC 4291), and RFC 2526 reserves 128 interface IDs near the top of every subnet for other anycast uses (in a /64, ::fdff:ffff:ffff:ff80 through ::fdff:ffff:ffff:ffff), so avoid assigning either to hosts. This calculator handles hexadecimal IPv6 notation and CIDR prefixes; embedded IPv4 dotted-quad notation and zone IDs are not accepted.
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How it works
An IPv6 address is 128 bits, written as eight groups of four hex digits. The prefix length says how many of those bits name the network. The rest are host bits, and a /64 leaves 64 of them, which is 264 addresses.
The calculator clears the host bits to find the network, sets them all to 1 to find the last address, and shows the address in both short form (with :: for the longest run of zero groups) and full form.
The child prefix answers "how many smaller networks fit inside this one?" Each extra prefix bit doubles the count, so a /48 split into /64s gives 216 = 65,536 subnets.
Worked example
Say your provider gives you 2001:db8:abcd::/48 (2001:db8:: is the range reserved for documentation):
Swipe the table sideways to see all columns ->
| Split into | Count | Typical use |
|---|---|---|
| /56 | 256 | One per site or building |
| /64 | 65,536 | One per VLAN |
The first /64 is 2001:db8:abcd::/64, the next is 2001:db8:abcd:1::/64, and so on up to 2001:db8:abcd:ffff::/64. The fourth group is simply the subnet number in hex, which makes IPv6 plans easy to read.
Why is every LAN a /64?
Stateless address autoconfiguration (SLAAC) builds each device's address from a 64-bit interface ID, so it only works on a /64. Using a smaller subnet on a LAN breaks it for many devices.
What size will my ISP give me?
Commonly a /48 or /56 for a business and a /56 or /64 for home service. Ask for at least a /56 if you plan more than one VLAN.
Is there a broadcast address?
No. IPv6 uses multicast instead, so the first and last addresses in a subnet are not reserved for network and broadcast the way they are in IPv4 (the all-zeros address is the subnet-router anycast).
Maintained by the RACKCRUNCH team. Last reviewed September 29, 2026. How we calculate | Report a problem