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IPv6 ULA Generator
The IPv6 ULA generator produces RFC 4193-compliant Unique Local Addresses for use in private IPv6 networks. A ULA prefix (fc00::/7, in practice fd00::/8) is the IPv6 equivalent of private IPv4 ranges like 192.168.0.0/16. The tool generates a random 40-bit Global ID and assembles a /48 prefix that is statistically unique and suitable for use in internal infrastructure.
What are IPv6 Unique Local Addresses?
IPv6 Unique Local Addresses (ULAs) are defined in RFC 4193 as the IPv6 equivalent of private IPv4 address ranges. They occupy the fd00::/8 prefix (the full fc00::/7 range, but fc::/8 is currently unassigned). ULAs are not routable on the public internet and are intended for use within a site or organization. Unlike IPv4 private addresses, ULAs include a randomly generated 40-bit Global ID that makes collisions between different organizations' private ranges extremely unlikely, which is important when merging networks or using VPNs.
How does it work?
The generator creates a cryptographically random 40-bit Global ID, prefixes it with fd (the L=1 variant of fc00::/7), and produces a /48 prefix in the form fd[GlobalID]::/48. This /48 prefix provides 65,536 /64 subnets, each capable of hosting a practically unlimited number of hosts using SLAAC. The tool displays the prefix, the full address range, and example subnet allocations for documentation purposes.
Typical Use Cases
- Assigning private IPv6 addresses to internal servers and services
- Configuring a home lab or office network with IPv6 that does not require ISP-assigned addresses
- Generating a stable private prefix for a VPN or site-to-site tunnel
- Designing an IPv6 addressing plan for an internal datacenter
Step-by-step Guide
- Step 1: Click Generate to create a new random Global ID.
- Step 2: Review the generated /48 ULA prefix.
- Step 3: Assign /64 subnets from within the /48 to your network segments.
- Step 4: Copy the prefix for use in your router or DHCP configuration.
Example
Input
Generate ULA
Output
fd3f:a2b1:c9d4::/48 — 65536 available /64 subnets
Tips & Notes
- Always generate a new random Global ID rather than using a manually chosen one — the randomness prevents collisions when connecting to other networks.
- Use /64 subnets within your /48 for each network segment — this is the standard IPv6 host subnet size.
- Document your ULA prefix allocation in your network diagram to avoid conflicts when adding new segments.
Frequently Asked Questions
What is the difference between ULA and link-local addresses (fe80::)?
Link-local addresses (fe80::/10) are only valid on a single network segment and cannot be routed even within a private network. ULA addresses are routable within your organization and can traverse internal routers, making them suitable for site-wide or multi-site private addressing.
Should I use ULA or global unicast addresses for internal services?
Both are valid. ULA provides stable addresses independent of your ISP, which is useful if you renumber for a new ISP. Global unicast addresses (your ISP-assigned prefix) are usable internally too. For production, many organizations use both and apply policy routing.
IPv6 ULA Generator
Generate unique local IPv6 addresses (ULA) per RFC 4193 — with random Global ID, subnet selection, and a full prefix overview.
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