IPv6 ULA generator
Generate IPv6 Unique Local Addresses (ULA)
Generated ULA Prefix
Subnets
Example subnets (/64)
RFC 4193 defines Unique Local Addresses (ULAs) for use within private networks.
The fd::/8 range (L=1) uses a randomly generated 40-bit Global ID — collision probability with other networks is extremely low.
ULAs are not routable on the public internet but are unique enough to avoid conflicts when merging networks.
TL;DR
What is IPv6 ULA generator?
IPv6 Unique Local Addresses (ULA) are the IPv6 equivalent of IPv4 private addresses. They are defined in RFC 4193 and use the prefix fd00::/8. ULAs are not routed on the public internet and are intended for use within a site or organization's internal network.
How it works
A ULA is formed by combining the fd prefix (indicating a locally assigned address), a randomly generated 40-bit global ID, a 16-bit subnet ID, and a 64-bit interface identifier. The random global ID makes collisions between different organizations' ULA ranges extremely unlikely.
Common use cases
- ‣Internal networking: assign stable IPv6 addresses to servers and services within a private network
- ‣Lab and homelab: set up IPv6 connectivity in an isolated environment without needing a public prefix
- ‣VPN addressing: use ULAs for internal addressing in a site-to-site VPN where public IPv6 is not available
Frequently asked questions
What is the difference between ULA and link-local addresses?
Link-local addresses (fe80::/10) are automatically assigned to every IPv6 interface and are only valid within a single network segment; they cannot be routed even within a private network. ULAs are routable within an organization's internal network and can cross routers.
Should I use ULA or global unicast addresses for internal services?
If your ISP provides a delegated IPv6 prefix (GUA), prefer using that for internal services to avoid address translation. ULAs are a good fallback when no GUA is available or when you want addressing that is independent of your ISP prefix.