IPv6 ULA Generator

Generate unique local IPv6 addresses (ULA) per RFC 4193 with cryptographically random prefixes.

1. Click the "Generate" button to create a new random IPv6 ULA /48 prefix using cryptographically secure randomness. 2. Review the generated prefix in standard IPv6 notation (e.g., fd12:3456:789a::/48). 3. View the breakdown showing the fd prefix byte, 40-bit random global ID, and available /64 subnet space. 4. Generate example subnet addresses by specifying a subnet ID to see a complete /64 prefix for a specific VLAN or segment. 5. Copy the generated ULA prefix to use in your router, DNS, or firewall configuration files.

About This Tool

The IPv6 ULA (Unique Local Address) Generator creates private IPv6 address prefixes following RFC 4193. These addresses are the IPv6 equivalent of private IPv4 ranges (like 10.0.0.0/8) and are designed for use within a site or between a limited number of sites. Each generated prefix is statistically unique, minimizing the risk of conflicts if networks are later merged.

ULA addresses use the fd00::/8 prefix followed by a 40-bit random identifier, creating a /48 prefix that you can further subnet as needed. This tool uses the Web Crypto API to generate cryptographically secure random values, ensuring high-quality randomness for the global ID portion.

This is particularly useful when setting up internal IPv6 networks that do not require global routability but need stable, predictable addresses for services, DNS, and internal communication.

Frequently Asked Questions

A Unique Local Address (ULA) is an IPv6 address intended for local communications within a site. Similar to private IPv4 addresses, ULAs are not routable on the global internet. They use the fd00::/8 prefix and are defined in RFC 4193.

ULA addresses are designed to be statistically unique by using a 40-bit random global ID. While not guaranteed unique like globally assigned addresses, the probability of collision is extremely low - roughly 1 in a trillion.

Use ULA for internal services that should not be reachable from the internet, such as internal DNS, file servers, or management interfaces. Global addresses should be used for services that need internet connectivity.

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