IPv6 ULA Generator
NetworkGenerate IPv6 unique local addresses in the fd00::/8 range with a custom subnet ID and EUI-64, for homelabs and private networks that stay stable over time.
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About IPv6 ULA Generator
IPv6 Unique Local Addresses (ULA, fc00::/7) are the IPv6 equivalent of private addresses — for internal use and never routed on the public Internet. Per RFC 4193, a proper ULA prefix sits under fd00::/8 and uses a random 40-bit Global ID so different sites almost never collide. This tool generates spec-compliant /48 ULA prefixes and splits /64 subnets locally in your browser with no network access — ideal for planning internal IPv6 addressing.
How to Use
- Open the IPv6 ULA Generator tool
- Enter the address or query parameters
- Adjust the output options as needed
- Click the Query button; results appear in real time
- Copy or export the result
Use Cases
- Internal addressing — Generate a stable /48 ULA prefix for a home or company network, independent of the ISP.
- Subnet planning — Carve multiple /64 subnets under a /48 for different VLANs or segments.
- Site interconnect — Produce low-collision ULAs for multi-site VPNs to avoid clashes when merging.
- Lab environments — Use local addresses that never leak to the public Internet when building an IPv6 lab.
- Dual-stack transition — Carry internal services over ULA while public traffic uses global addresses.
- Container networks — Generate a /64 per Docker or Kubernetes pod range so each tenant gets a unique local segment.
- Collision check — Compare generated ULAs against your existing site prefixes to confirm no overlap before deployment.
FAQ
How does ULA differ from link-local (fe80::)?
fe80::/10 link-local addresses are valid only on a single link and cannot cross routers; ULA (fd00::/8) routes across an entire site between subnets but, like link-local, is never routed on the public Internet.
Why do generated prefixes start with fd?
ULA spans fc00::/7; with the L bit set to 1 (i.e., fd00::/8), the Global ID is locally and randomly assigned, as RFC 4193 recommends. fc00::/8 is reserved for future central allocation and is not yet in use.
Why must the Global ID be random?
A random 40-bit Global ID makes collisions between different organizations' ULA prefixes extremely unlikely, so addresses rarely clash when sites merge or VPNs interconnect.
How many /64s fit in one /48?
From /48 to /64 there are 16 subnet bits, allowing 65,536 /64 subnets — ample for most internal networks.
Can a ULA reach the public Internet directly?
No. ULAs are designed not to be routed publicly; Internet access still needs a global unicast address (GUA) or NAT/NPT translation.