IPv6 ULA Prefix Generator

Generates an IPv6 Unique Local Address (ULA) prefix per RFC 4193.

How to use

1. Switch to the IPv6 tab and scroll to the IPv6 ULA Prefix Generator panel.
2. Optionally enter a 10-character hex Global ID (40 bits). Leave blank to generate one pseudo-randomly.
3. Click Generate ULA Prefix.

Output

A /48 prefix starting with fd (the ULA range fc00::/7 with L-bit set). For example:

fd12:3456:789a::/48

The panel also shows:

• The Global ID used
• Five example /64 subnets derived from the prefix

Global ID

The 40-bit global ID is the locally significant portion of the ULA prefix. RFC 4193 recommends deriving it pseudo-randomly so it is globally unique with high probability. You can supply your own value for reproducibility (e.g. to regenerate a prefix from an existing network plan).

Warning

ULA prefixes are not globally routable. They are intended for use within a private network and should not appear in BGP routing tables.