Open Source Tools

IPv6 Subnet Calculator

Supply an IPv6 address and prefix, then choose a child prefix to see how the allocation can be divided. Address counts remain exact even for the entire IPv6 space.

Use a value at least as large as the parent prefix, up to 128.

Full and compressed hexadecimal addresses are accepted, including a dotted IPv4 suffix. Omit brackets, ports, and interface identifiers.

Parent network

2001:db8:1234::/48

Compressed input address
2001:db8:1234:5678::1
Expanded input address
2001:0db8:1234:5678:0000:0000:0000:0001
Range starts
2001:db8:1234::
Range ends
2001:db8:1234:ffff:ffff:ffff:ffff:ffff
Addresses in parent
1,208,925,819,614,629,174,706,176
Child subnet count
65,536

Child prefixes (first 8)

  • 2001:db8:1234::/64
  • 2001:db8:1234:1::/64
  • 2001:db8:1234:2::/64
  • 2001:db8:1234:3::/64
  • 2001:db8:1234:4::/64
  • 2001:db8:1234:5::/64
  • 2001:db8:1234:6::/64
  • 2001:db8:1234:7::/64

How many subnets fit?

Subtract the parent prefix length from the child length and raise two to that difference. Dividing a /48 into /64 networks gives 65,536 child blocks. Each /64 spans 18,446,744,073,709,551,616 addresses. The preview shows the earliest eight children rather than attempting to list the full allocation.

Unlike IPv4, IPv6 does not define a broadcast address. The endpoints shown here are mathematical boundaries, not a promise that every address is assignable to a host. Address architecture and anycast reservations still apply.

Compressed input, explicit boundaries

A double colon replaces omitted zero groups and can appear once in an address. The output compresses the longest zero run, choosing the first run when lengths tie. Single zero groups stay visible. An expanded view makes all eight groups inspectable.

For example, 2001:db8:1234:5678::1/48 belongs to 2001:db8:1234::/48. Its first /64 child is 2001:db8:1234::/64. The documentation prefix 2001:db8:: is useful for examples; it is not a public allocation for your equipment. Zone identifiers such as %eth0 and bracketed host-and-port strings are outside this input format.