IPv6 ULA Generator — Free Unique Local Address Generator (RFC 4193)

IPv6 ULA Generator — Free Unique Local Address Generator (RFC 4193). Free online IPv6 ULA generator. Enter your MAC address to instantly generate an RFC 4193 compliant unique local IPv6 address with /48 prefix and /64 subnet blocks.

Generate IPv6 ULA (Unique Local Address) prefixes instantly with our free online IPv6 ULA generator.

Enter your device MAC address to get an RFC 4193 compliant /48 unique local address with first and last /64 subnet blocks — all computed in your browser with no data sent to any server.

Perfect for network engineers creating IPv6 private address spaces, VPN tunnel isolation, lab environments, and IoT device segmentation.

Our IPv6 ULA generator follows the RFC 4193 section 3.2.2 algorithm: the current time in 64-bit NTP format and an EUI-64 identifier derived from your MAC address are hashed with SHA-1, and the lowest 40 bits become the Global ID after fd.

RFC 4193 prefixes are pseudo-random rather than guaranteed unique — for any two networks the chance of drawing the same /48 is about 1 in 1.1 trillion — which is why RFC 4193 calls them globally unique only with high probability.

Click Generate again for a fresh prefix. All generation runs client-side so your internal network topology stays private. Also try our IPv6 Subnet Calculator, IPv4 Subnet Calculator, and MAC Address Generator for a complete networking toolkit.

Frequently asked questions

How do I generate an IPv6 unique local address?

Type a MAC address such as 20:37:06:12:34:56 into the MAC Address field. The tool immediately shows an IPv6 ULA /48 prefix starting with fd, plus the First /64 block and Last /64 block of that prefix, each with a copy button.

How is the ULA prefix calculated?

It follows RFC 4193 section 3.2.2: the current time as a 64-bit NTP timestamp is joined with an EUI-64 identifier made from your MAC address, the result is hashed with SHA-1, and the lowest 40 bits become the Global ID behind fd. The prefix is pseudo-random, so a clash with another network is very unlikely but not impossible.

Why do I get a different prefix for the same MAC address?

Because the current time is part of the hash, the result changes every time it is recalculated, when you edit the MAC field or click Generate again. That is intended: the goal is a random prefix that is very unlikely to collide with another network. Copy the one you want and keep using it.

Which MAC address formats are accepted?

Use hexadecimal byte pairs separated by colons or dashes, for example 20:37:06:12:34:56 or 20-37-06-12-34-56. Other formats show Invalid MAC address and no result is displayed until the input is fixed.

What are the first and last /64 blocks?

A /48 ULA prefix holds 65536 subnets of size /64, numbered in the fourth group from 0 to ffff. The tool shows the first (subnet 0) and the last (subnet ffff) so you can see the range available for your VLANs or LANs.

Can a ULA be used on the public internet?

No. Unique local addresses (fc00::/7, in practice fd00::/8) are meant for private networks, much like IPv4 10.0.0.0/8, and are not routed on the public internet. They suit labs, VPNs and internal services.

How to use this online tool

IPv6 ULA Generator — Free Unique Local Address Generator (RFC 4193) is designed for fast browser workflows when you need to format, validate, convert, decode, encode, generate, or inspect data without opening a heavy desktop app. Start with the input field or visible options, review the result, then copy or download the output for the next step.

Private processing in your browser

IPv6 ULA Generator — Free Unique Local Address Generator (RFC 4193) keeps the normal processing step local in your browser. That is useful for code snippets, tokens, documents, configuration values, text samples, and other material that should not be sent to a remote service unless you explicitly choose to share it.

When this tool is useful

Use IPv6 ULA Generator — Free Unique Local Address Generator (RFC 4193) for repeatable developer tasks, technical documentation, QA checks, quick conversions, debugging, content cleanup, and internal team workflows. The page focuses on clear inputs, immediate feedback, and output that is easy to reuse in code, reports, tickets, emails, or notes.

Practical tips

Before copying the final result, check important details such as spacing, casing, filenames, encoding, token structure, line breaks, or output format. Small checks prevent mistakes when the result is reused in source code, API requests, documentation, spreadsheets, or shared files.