IPv6 ULA Generator

Generates a proper RFC 4193 address — not just a random string with colons

A lot of people reach for fc00:: or just make something up when they need an internal IPv6 address, and that tends to cause problems later. RFC 4193 specifies that locally assigned addresses should use the fd prefix with a randomly generated 40-bit Global ID, which makes collisions between different networks unlikely enough to not matter in practice. That's what this generates. Each result shows the full address broken down into its components — the prefix, Global ID, Subnet ID, and Interface ID — so you can see which part is which before you put it into a config. Set the count anywhere from 1 to 100 if you need a batch.

When a ULA is the right choice and when it isn't

Link-local (fe80::/10) only works on a single network segment — it doesn't survive a router hop, so it's useless for anything spanning multiple VLANs or subnets. Public addresses work everywhere but they depend on your ISP and change if you move providers. A ULA sits in between: it routes across your internal infrastructure without touching the internet, and it stays stable regardless of what happens upstream. For homelabs, internal DNS, Docker networks, and VPN configurations where you need stable addressing that doesn't require a public prefix, ULAs are the right call. The one thing they don't help with is any service that legitimately needs to be reachable from outside your network — for that you still need a public address.