IPv6 ULA Generator

Generate RFC 4193 Unique Local Addresses. Create /48 prefixes, enumerate /64 subnets, and validate ULA addresses. 100% client-side.

Last reviewed: April 2026
Reviewed by , software engineer · last updated April 2026

New to this tool? Click here for instructions

Raw Output
Click Generate Prefix to create a new RFC 4193 ULA prefix.

How to Use the IPv6 ULA Generator

The IPv6 ULA Generator is a free online tool that allows you to generate RFC 4193 Unique Local Addresses (ULAs). ULAs are used within private networks where global reachability is not needed. To use the generator, simply enter a /48 ULA prefix and choose how many /64 subnets to enumerate. The tool will display the compressed and expanded address forms, a bit-level breakdown, and an optional example host address within the prefix.

  • Enter a /48 ULA prefix (e.g. fd12:3456:7890::/48)
  • Choose how many /64 subnets to enumerate
  • View the compressed and expanded address forms
  • See a bit-level breakdown of the address
  • Get an example host address within the prefix

When to Use the Tool in Real Workflows

The IPv6 ULA Generator is ideal for network administrators and IT professionals who need to manage private networks. It's particularly useful for documenting subnet allocations, planning VLAN assignments, and ensuring that ULAs are correctly configured within a network.

How It Works

The tool uses a simple and efficient algorithm to generate RFC 4193 ULAs. It ensures that the Global ID is randomly generated, making the probability of two independent sites choosing the same prefix negligibly small. The tool also provides options to enumerate /64 subnets and validate IPv6 addresses, making it a comprehensive solution for managing private IPv6 networks.

Tips, Edge Cases, or Limitations

While the tool is designed to be user-friendly, it's important to understand that it operates entirely in the browser and does not require any server-side processing. This ensures that your data remains private and secure. Additionally, the tool assumes that the input is a valid /48 ULA prefix. If you enter an invalid prefix, the tool will not be able to generate subnets or validate addresses.

Frequently Asked Questions

An IPv6 Unique Local Address (ULA) is the IPv6 equivalent of IPv4 private address space. Defined in RFC 4193, ULAs occupy the fc00::/7 block and are not routable on the global internet. They are designed for use within private networks.
A ULA address has four parts: Prefix (8 bits), Global ID (40 bits), Subnet ID (16 bits), and Interface ID (64 bits). The Prefix is always fd for locally generated addresses, and the Global ID is a randomly generated 40-bit value.
The fc00::/8 block is reserved for centrally assigned Global IDs, while the fd00::/8 block is used for locally generated ULAs. The IETF has discussed deprecating fc00::/8 in favor of expanding the locally assigned range, but for now, always use fd as your prefix byte.
No, ULA addresses and IPv6 link-local addresses are different. Link-local addresses (fe80::/10) are auto-configured on every interface but cannot cross routers. ULA addresses (fc00::/7) can be routed within a private network, making them suitable for multi-site VPN topologies or internal service meshes.
With 16 bits for the Subnet ID, a /48 ULA prefix can provide up to 65,536 /64 subnets.