About IPv6 ULA
Use IPv6 ULA to Local IPv6 Gen. The tool runs in your browser for fast results and keeps your data local.
How to Use
- 1. Add your input or data.
- 2. Adjust options if needed.
- 3. Review the result and copy it.
What is IPv6 ULA?
IPv6 Unique Local Addresses (ULA) are private IPv6 addresses defined in RFC 4193, analogous to IPv4 private addresses (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16). ULA addresses use the fc00::/7 prefix, with fd00::/8 for locally assigned addresses. A ULA consists of a 40-bit Global ID (randomly generated), a 16-bit Subnet ID, and a 64-bit Interface ID. ULAs are not routable on the public internet, making them suitable for internal networks, VPNs, and private communications. Unlike IPv4 NAT, ULAs provide end-to-end connectivity within private networks while maintaining address uniqueness through random Global ID generation.
Common Use Cases
IPv6 ULA addresses are essential for private IPv6 networking. Enterprise networks use ULAs for internal services that should not be internet-accessible. VPN administrators assign ULA addresses for secure private communications. Home networks use ULAs for local device communication without internet exposure. Data centers use ULAs for management networks and internal infrastructure. IoT deployments use ULAs for device-to-device communication within private networks. Development environments use ULAs for isolated testing without internet connectivity. Disaster recovery sites use ULAs for site-to-site VPN connections.
- Enterprise internal services not internet-accessible
- VPN private communications and tunnels
- Home network local device communication
- Data center management networks
- IoT device-to-device private communication
- Development and testing isolated environments
- Disaster recovery site-to-site VPNs
- Private cloud infrastructure networking
Best Practices & Tips
Generate the 40-bit Global ID randomly to ensure uniqueness across networks. Use fd00::/8 prefix for locally assigned ULAs (fc00::/8 is reserved for future use). Document your ULA prefix to maintain consistency across the organization. Use ULAs alongside Global Unicast Addresses (GUA) for dual addressing. Configure routing to prevent ULA leakage to the internet. Use /48 prefixes for sites, /64 for subnets as per RFC recommendations. Avoid renumbering ULA prefixes—generate once and keep consistent. Use ULAs for stable internal addressing independent of ISP changes.
- Generate 40-bit Global ID randomly for uniqueness
- Use fd00::/8 prefix (fc00::/8 reserved for future)
- Document ULA prefix for organizational consistency
- Use ULAs alongside GUAs for dual addressing
- Configure routing to prevent internet leakage
- Use /48 for sites, /64 for subnets
- Avoid renumbering—generate once, keep consistent
- Use for stable addressing independent of ISP
Troubleshooting Common Issues
If ULA addresses leak to the internet, configure firewall rules to block fc00::/7 on external interfaces. If devices cannot communicate, verify routing is configured for ULA prefixes. If address conflicts occur, regenerate the Global ID—collisions are extremely rare with proper random generation. If dual-stack issues arise, ensure both ULA and GUA addresses are properly configured. If DNS resolution fails, configure DNS servers to handle ULA addresses. If VPN connections fail, verify both ends use compatible ULA addressing. If routing loops occur, check for improper ULA route advertisements.
- ULA addresses leaking to internet without firewall rules
- Devices unable to communicate due to missing routes
- Address conflicts from non-random Global ID generation
- Dual-stack configuration issues with ULA and GUA
- DNS resolution failures for ULA addresses
- VPN connection issues with incompatible ULA addressing
- Routing loops from improper route advertisements
- ISP blocking or filtering ULA traffic incorrectly
Frequently Asked Questions
Is IPv6 ULA free to use?
Yes. IPv6 ULA is free and works directly in your browser.
Does IPv6 ULA upload my data?
No. Most processing happens locally. Any network requests are clearly indicated.
What formats does IPv6 ULA support?
IPv6 ULA supports the common formats described on the page. Convert uncommon formats before pasting.
How should I share results from IPv6 ULA?
Copy the output and review any sensitive data before sharing or publishing.