This tool checks the written address and prefix, but it also explains the result. IPv6 has no broadcast address, so the first and final values shown below are boundaries of the prefix rather than IPv4-style network and broadcast reservations.
Calculate an IPv6 address and prefix
Include the prefix in the address, or enter it separately. The child prefix is optional and shows how the parent can be divided into smaller prefixes.
IPv6 results
- Normalized input
- Recommended compressed form
- Fully expanded form
- Containing prefix
- First address in prefix
- Final address in prefix
- Containing /64
- Prefix bits
- Bits after the prefix
- Matched address range
- Embedded IPv4 address
Address type:
Child-prefix plan
- Number of child prefixes
- Selected child number
- Child containing the entered address
- Previous child prefix
- Next child prefix
First child prefixes
128-bit group view
| Group | Hex | Binary | Role for this prefix |
|---|
How this result was calculated
How to read the results
The recommended compressed form follows RFC 5952: remove leading zeros, use lowercase hexadecimal, and replace the longest run of at least two zero groups with ::. The fully expanded form shows all eight groups and all four digits in each group.
The containing prefix clears every bit after the slash length. The final address sets those remaining bits to 1. These values describe the numeric boundaries of the prefix. IPv6 does not have a broadcast address, and the boundary values are not automatically treated like IPv4 network and broadcast addresses.
The address type identifies common special-purpose ranges such as link-local, unique-local, multicast, documentation, loopback, and translation prefixes. A global-unicast result does not prove that the address is assigned, reachable, or allowed through a firewall.
How child-prefix planning works
The child prefix must be equal to or longer than the parent. The difference tells the calculator how many bits are available to number child prefixes.
Parent /48 to child /64
64 - 48 = 16 child-prefix bits
2^16 = 65,536 child /64 prefixesThe entered address selects one child prefix. In the example, 2001:db8:1234:12ab::20/48 falls inside 2001:db8:1234:12ab::/64. The value 12ab is the child number in hexadecimal. The calculator also shows the decimal index and the neighboring prefixes.
Clear the child-prefix field when you only need to analyze the address and its current prefix.
What the /64 result means
A /64 is the normal size for many IPv6 LANs and is expected by common Stateless Address Autoconfiguration designs. Routing still supports other prefix lengths, so a prefix is not invalid merely because it is shorter or longer than /64.
The calculator always shows the containing /64 because it helps with address reading and common LAN planning. When the entered prefix is longer than /64, that result is a broader parent prefix rather than the exact calculated prefix.
For a full explanation of address types, compression, SLAAC, DHCPv6, Neighbor Discovery, and planning examples, use the IPv6 Addressing and Prefix Reference.
What this tool does not verify
- It does not confirm address ownership, allocation, routing, firewall policy, DNS, or internet reachability.
- It recognizes common address categories but does not replace the complete IANA special-purpose registry.
- It removes zone identifiers such as
%eth0from consideration. A zone identifies the local interface or scope context, not part of the 128-bit address. - It does not decide whether every address inside a prefix should be assigned. Architecture, anycast use, platform behavior, and policy still matter.
- It does not generate modified EUI-64 interface identifiers, reverse-DNS names, or route summaries.