IPv6 ULA Generator

Generate random IPv6 Unique Local Addresses (ULA) per RFC 4193. Produces a /48 prefix with global ID and optional /64 subnet.

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How to Use This Tool

Set how many ULA prefixes to generate (up to 10) and click Generate. Each result includes the /48 site prefix, the 40-bit Global ID, and an example /64 subnet.

Common Use Cases

  • Assign a private IPv6 address space to a home or office network
  • Set up IPv6 in a lab environment without a public prefix
  • Prepare for IPv6 deployment by reserving internal address space
  • Create isolated IPv6 segments for containers or VMs

Frequently Asked Questions

What is a ULA (Unique Local Address)?

A ULA is an IPv6 address in the fc00::/7 range, defined by RFC 4193. ULAs are intended for local communications within a site and are not routable on the global internet, similar to RFC 1918 private IPv4 addresses (10.x.x.x, 192.168.x.x).

Why does the prefix start with 'fd'?

The fc00::/7 block is split into two halves. The 'fc00::/8' half (L=0) is reserved for future use. The 'fd00::/8' half (L=1) is for locally assigned addresses generated with a random global ID — which is what this tool produces.

What is the Global ID?

The Global ID is a 40-bit randomly generated value that makes the ULA prefix unique to your site. It occupies bits 8–47 of the address. Because it is random, the probability of collision with another site's ULA is extremely low.

What is the /48 prefix used for?

The /48 prefix (fd + Global ID) is the site prefix. Within it you can create up to 65,536 subnets (/64 each) using the 16-bit Subnet ID field. Each /64 subnet can hold a virtually unlimited number of hosts.