What is IPv6 ULA Prefix Generator Online?
As organizations transition to IPv6, they still often need private address space for internal networks that should never be reachable from the public internet. IPv6 Unique Local Addresses (ULA), as defined in RFC 4193, are the modern equivalent of IPv4's private ranges (like 10.0.0.0/8). Our IPv6 ULA prefix generator online tool helps you created a valid local prefix starting with "fd00::/8," complete with a 40-bit cryptographically random Global ID. Generating a random Global ID is a critical part of the RFC 4193 specification. It ensures that if two private networks are eventually merged—such as during a company acquisition—the probability of an address collision is statistically near zero. This tool automates the random ID generation and correctly formats the resulting /48 prefix, which you can then subdivide into over 65,000 individual /64 subnets for your local infrastructure. Everything is generated locally on your machine, ensuring that your private network prefixes remain exactly that—private. It is an essential utility for network architects, system administrators building test labs, and cloud engineers configuring private VPC segments who want to follow the latest industry best practices for IPv6 deployment.
How to Use IPv6 ULA Prefix Generator Online
- Click the 'Generate' button to create a new, random RFC 4193 compliant ULA prefix.
- Use the provided /48 prefix as the base for your internal network.
- Subdivide the prefix into /64 subnets for specific VLANs or departments.
Developer Tips
When configuring ULA addresses on your servers, remember that IPv6-capable OSs will often prefer a public GUA (Global Unicast Address) over a ULA for outgoing traffic. You may need to tune the label preference policy in `/etc/gai.conf` if you want internal traffic to stay on the ULA network.
Frequently Asked Questions
Are ULA addresses routable on the public internet?
No. IPv6 ULA addresses (fc00::/7) are designed for local use only. Routers are configured by default to never forward these packets beyond the local site boundary.
What is the difference between fc00:: and fd00::?
The ULA space is fc00::/7. However, the first half (fc00::/8) is reserved for future global assignment. Currently, all locally assigned random prefixes must start with fd00::/8.