IPv6 ULA Generator

What Is an IPv6 ULA Generator?

An IPv6 Unique Local Address (ULA) Generator creates random fd00::/8 addresses according to RFC 4193. Unlike global unicast addresses, ULAs are intended for local communication within a site or organization and are not expected to be routable on the global internet. This makes them ideal for internal networks, VPNs, lab environments, and private infrastructure where you need IPv6 connectivity without requesting a public prefix.

How to Use the IPv6 ULA Generator

Enter a valid MAC address (e.g., 20:37:06:12:34:56). The tool combines the current timestamp with your MAC address, computes a SHA1 hash, and extracts the lower 40 bits to generate a random 48-bit global ID prefix. The result is an IPv6 ULA in fdxx:xxxx:xxxx::/48 format, along with the first and last routable /64 subnets within that prefix.

Why Use ULAs?

Unique Local Addresses offer several advantages over other IPv6 address types for private networking. They are globally unique (the probability of two independently generated ULAs colliding is extremely low), they work without any upstream provider or DHCP infrastructure, and they can be used alongside global addresses (via privacy extensions or multi-homing). This makes ULAs a best practice for internal services, Docker networks, Kubernetes clusters, and site-to-site VPNs.

How ULA Generation Works

RFC 4193 specifies that the 40-bit global ID should be generated pseudo-randomly. The IETF recommends using a SHA1 hash of the current timestamp combined with a site-specific identifier (such as a MAC address) to produce the global ID. The tool takes the last 40 bits (10 hex characters) of this hash and prepends the fd prefix to form a /48 ULA prefix. From this prefix, you can create up to 65536 /64 subnets for your internal network segments.

Work with other address formats using the IPv4 to IPv6 Converter, IPv6 to Binary Converter, or MAC Address Analyzer.