About this tool
IPv6 addresses are 128 bits long, so compressed notation is essential for readability. Zero runs can be shortened with :: and leading zeros inside a hextet can be omitted. The underlying address still represents the same 128-bit value.
This tool normalizes an address, shows its expanded form and calculates the network prefix for the supplied prefix length. It is useful for validating documentation, interface addressing and routed prefixes.
How to use it
- Enter an IPv6 address and prefix, such as 2001:db8:1234:5678::1/64.
- Calculate.
- Use the normalized and expanded forms to compare addresses or document the prefix consistently.
Example: 2001:db8:1234:5678::1/64
The expanded address is 2001:0db8:1234:5678:0000:0000:0000:0001. With a /64 prefix, the network portion is 2001:db8:1234:5678::/64.
Engineering notes
- A /64 is the normal subnet size for many IPv6 LANs because several IPv6 mechanisms assume a 64-bit interface identifier.
- Do not remove leading zeros from the middle of a hextet in a way that changes its value; only leading zeros may be omitted. The :: abbreviation can appear only once in an address.
Frequently asked questions
Why is IPv6 written in hexadecimal?
Hexadecimal represents binary compactly: each hex digit maps to four bits, which makes 128-bit addresses manageable.
What does :: mean?
It replaces one or more consecutive 16-bit groups of zeros.
Is /64 always required?
No, but it is the standard size for many host subnets. Point-to-point links, loopbacks and routed allocations may use different prefix lengths.