Quick example
Calculate the subnet for 2001:db8:1234:5678::abcd/64
With a /64 prefix, the first 64 bits identify the network. The resulting CIDR is 2001:db8:1234:5678::/64, and the final address is 2001:db8:1234:5678:ffff:ffff:ffff:ffff.
Prefix scale
Common IPv6 prefix sizes and address counts
Every additional prefix bit halves the address block. These examples show how quickly IPv6 address counts change.
| Prefix | Network bits | Host bits | Total addresses |
|---|---|---|---|
| /32 | 32 | 96 | 79,228,162,514,264,337,593,543,950,336 |
| /48 | 48 | 80 | 1,208,925,819,614,629,174,706,176 |
| /56 | 56 | 72 | 4,722,366,482,869,645,213,696 |
| /64 | 64 | 64 | 18,446,744,073,709,551,616 |
| /96 | 96 | 32 | 4,294,967,296 |
| /128 | 128 | 0 | 1 |
Reading the result
What the IPv6 subnet values mean
Normalized and expanded address
The normalized form compresses the longest run of zero hextets. The expanded form writes all eight hextets with four hexadecimal digits each.
Network CIDR
The network address has every host bit set to zero. Appending the prefix length produces the canonical CIDR block for the entered address.
First and last address
The first address sets every host bit to zero, while the last sets every host bit to one. Together they define the complete numeric boundary.
Host bits and address count
Subtract the prefix from 128 to find the host bits, then raise 2 to that power to calculate the exact number of addresses.
Important difference
IPv6 does not use broadcast addresses
Unlike IPv4, IPv6 does not reserve a broadcast address at the end of a subnet. The calculator therefore reports the final address in the block rather than labeling it as broadcast. IPv6 uses multicast for traffic that needs to reach groups of interfaces.
Common questions
IPv6 subnet calculator FAQ
Does IPv6 have a broadcast address?
No. IPv6 uses multicast instead, so this calculator reports the first and last numeric addresses in the subnet.
How many addresses are in an IPv6 /64?
A /64 leaves 64 host bits and contains exactly 18,446,744,073,709,551,616 addresses.
Does :: change the value of an IPv6 address?
No. It replaces one or more consecutive zero hextets. The compressed and expanded forms still represent the same 128-bit value.