IPv6 ULA Generator
Generate an IPv6 Unique Local Address /48 prefix with RFC 4193-style Global ID and subnet planning output.
IPv6 ULA Generator creates an RFC 4193 Unique Local Address prefix for private IPv6 networks. The recommended mode uses cryptographically secure random bytes to create a 40-bit Global ID under fd00::/8. A MAC-address plus current-time option is also available for compatibility with the traditional RFC-style generation approach used by the legacy CI3 tool.
ULA prefixes are intended for internal routing, labs, VPNs, site-to-site networks, and private infrastructure. They are not meant to be advertised to the public internet.
IPv6 ULA Generator
Enter the required values and run the tool to view results.
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How to use IPv6 ULA Generator
Choose the generation method and run the tool. For most networks, use the random Global ID option. If you need legacy-style generation, choose MAC address plus current time and enter a valid 48-bit MAC address such as 20:37:06:12:34:56. The result includes the generated /48 prefix, the first and last routable /64 subnet, an example subnet, an example router address, and a reverse DNS zone for the prefix.
What is an IPv6 ULA?
A Unique Local Address is IPv6 private-use addressing, similar in purpose to IPv4 private ranges such as 10.0.0.0/8 or 192.168.0.0/16, but with a much larger address space. Locally assigned ULA prefixes use fd00::/8 followed by a 40-bit Global ID and a 16-bit subnet ID, producing a normal /64 subnet for each LAN or VLAN.
Why generate a random Global ID?
The 40-bit Global ID is designed to make accidental overlap unlikely when private networks later merge, connect by VPN, or exchange routes. A strong random value is the preferred practical approach for new deployments because it avoids dependence on hardware identifiers and produces low collision risk.
How to plan subnets
The generated /48 contains 65,536 possible /64 subnets. Use one /64 per LAN, VLAN, VPN segment, or routed interface network. Avoid using subnets longer than /64 for ordinary LANs because many IPv6 features and host behaviors assume /64 network boundaries.
ULA deployment notes
Do not publish ULA prefixes in global BGP or use them for public services. For internet-reachable hosts, use provider-assigned or provider-independent global unicast IPv6 space. ULA is useful beside global IPv6 when you need stable internal addresses, private routing, management networks, or VPN-only addressing.
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