IPv6 ULA generator
Get a random IPv6 unique local address (ULA) prefix for your private network, as RFC 4193 asks. Or paste a prefix you already use to check it.
How it works
Unique local addresses (ULAs) are IPv6's private addresses, like 192.168.0.0/16 in IPv4. They work inside your network and are never routed on the internet. They all start with fd, followed by a 40-bit Global ID you pick at random. That gives your site its own /48 with 65,536 /64 subnets.
The Global ID must be random (RFC 4193). Then two networks that later merge, or join over a VPN, almost certainly won't clash. Hand-picked IDs like fd00::/48 or fd12:3456:789a::/48 are common, so they clash often. This page flags them. The other half of the range, fc00::/8, was kept for a central registry that never happened, so don't use it.
Each subnet is a /64, so devices can configure themselves with SLAAC (see MAC to IPv6). To split your /48 further, use the IPv6 subnet splitter or the IPv6 subnet calculator.