Generator
Generate an RFC 4193 unique local prefix, choose a subnet ID, and create a ready-to-use IPv6 address for private networks, labs, VPNs, or internal service environments.
Private IPv6 prefix builder
Generate a fresh global ID, then set the subnet and host portions you want to use inside your private IPv6 space.
RFC 4193 ULA prefixes start with fd plus a random 40-bit global ID.
Use one hextet to define a /64 inside the /48 prefix.
Add a simple host portion to build an example interface address.
ULA /48 prefix
fd12:3456:789a::/48
Use this as the top-level private prefix for your site or environment.
Derived /64 subnet
fd12:3456:789a:0001::/64
Most internal IPv6 networks use /64 subnets, so this is usually the practical next step.
Example host address
fd12:3456:789a:0001::0001
A ready example address you can adapt for documentation, lab setups, or internal testing.
How to Use This IPv6 ULA Generator
Generate a fresh RFC 4193 prefix, choose the subnet ID you want to work with, then copy the exact level you need for planning or implementation.
Generate a fresh ULA prefix
Start with a random RFC 4193 global ID so your internal IPv6 space is unlikely to collide with another private environment later.
Set the subnet ID you want to use
Pick a hextet like `0001`, `0010`, or `00ff` to derive a practical /64 subnet from the top-level /48 prefix.
Add a sample host portion
Use a simple host value to build a complete example address for documentation, tests, or internal service planning.
Copy the value that matches your next step
Take the /48 prefix, /64 subnet, or example host address directly into router config, internal DNS, or lab notes.
When This Tool Is Most Useful
It helps most when you want private IPv6 space that is safer to extend across labs, internal services, or linked private sites without relying on public addressing.
Private lab and home-lab networks
Create stable private IPv6 prefixes for isolated environments without reaching for public provider allocations.
Internal service and container addressing
Give internal apps, VPN links, or container networks a consistent IPv6 space that stays inside your private routing domain.
Merger and overlap avoidance
ULA prefixes reduce the risk of painful internal collisions when separate private networks eventually need to interconnect.
Documentation and architecture planning
Build realistic IPv6 examples for diagrams, network runbooks, or policy drafts without using real production prefixes.
FAQs
What is a ULA in IPv6?
A ULA is a Unique Local Address defined by RFC 4193. It is meant for private IPv6 use, similar in spirit to private IPv4 ranges.
Why generate a random global ID?
The random 40-bit global ID helps reduce collisions if private networks ever connect later through VPNs, mergers, or cross-site routing.
Why show a /64 subnet too?
Most real IPv6 LAN and internal segment designs use /64 boundaries, so showing a derived /64 is more practical than stopping at only a /48.
Does this tool send data anywhere?
No. The prefix generation happens in your browser so you can use it locally while planning private IPv6 space.