IPv6 ULA Prefix Generator

Generate RFC 4193 compliant IPv6 Unique Local Addresses (ULA) instantly. Create random 40-bit Global IDs and 16-bit Subnet IDs for private networking. 100% private.

ULA Configuration

Subnet ID (Hex)

Enter up to 4 hex characters (0-FFFF) to define your local subnet.

Generation History

No addresses generated yet.

What is a ULA?

Unique Local Addresses are the IPv6 equivalent of private IPv4 addresses (like 192.168.x.x). They are intended for local communications and are not routable on the public internet.

Randomness Requirement

RFC 4193 requires the Global ID to be generated randomly to minimize the risk of collisions when different local networks are merged (e.g., during company acquisitions).

Private Generation

Random seeds are generated using the browser's crypto.getRandomValues API. Your network identifiers never leave your device.

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How to Use

The Professional IPv6 ULA Generator is a compliant utility for creating private, non-routable address prefixes for local networks based on the RFC 4193 specification.

How to use this tool

Define Subnet: Enter a 4-character hexadecimal Subnet ID (e.g., 0001) to identify your local network segment.
Generate Prefix: Click "Generate New" to create a unique 40-bit Global ID. This is randomized using cryptographically secure methods.
Visual Breakdown: Review the bit-map visualizer to see how the prefix, Global ID, and Subnet ID combine to form the final /64 address.
Manage History: The tool keeps track of your last 10 generated prefixes. You can copy them individually or export the full list as a text file.
Configuration: Use the generated fdXX::/64 prefix in your router or server configuration for private internal communications.

About This Tool

What is an IPv6 ULA?

Unique Local Addresses (ULA) are intended for local use. They are not expected to be routable on the global internet, but are unique enough to be combined without address collisions. They replace the older "Site Local" addresses and the private ranges of IPv4 (like 10.x.x.x).

According to RFC 4193, these addresses must use the prefix fd00::/8. The subsequent 40 bits must be generated randomly to ensure that if two private networks are ever connected, the chance of an IP conflict is statistically negligible.

Why Use This Tool

Reliable Private Networking

Manually picking private IP ranges often leads to repetitive patterns (like fd00:1:1:1::) which cause massive headaches when joining networks later. Our generator enforces the RFC-mandated randomness, providing you with a high-entropy Global ID that adheres to best practices for modern IPv6 architecture.

FAQ

What is an IPv6 ULA address?

ULA (Unique Local Address) is the IPv6 equivalent of IPv4 private addresses (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16). They use the fd00::/8 prefix and are designed for local communication within an organization. Unlike IPv4 private addresses, ULAs include a random 40-bit Global ID that minimizes collisions between independent networks.

How is the random Global ID generated?

According to RFC 4193, the 40-bit Global ID should be generated using cryptographically secure random data. This tool uses the browser's Web Crypto API to generate a truly random ID, resulting in a prefix like fd12:3456:789a::/48 where the 40 bits after fd are random.

How many subnets can I create with a /48 ULA prefix?

A /48 prefix provides 16 bits for Subnet IDs, allowing up to 65,536 individual subnets (2^16). Each subnet has a 64-bit host address space, providing a virtually unlimited number of addresses.

Are ULA addresses routable on the Internet?

No. ULA addresses (fd00::/8) should not be routed on the public Internet. Transit routers should filter them. They are exclusively for internal use in private networks, similar to RFC 1918 addresses in IPv4.