Generate RFC 4193 compliant IPv6 Unique Local Addresses (ULA) and /64 subnets.
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About IPv6 ULA generator
Generates an IPv6 Unique Local Address prefix: fd followed by a 40-bit Global ID gives a /48, and a 16-bit Subnet ID gives each /64. The Global ID can come from a cryptographic random source or from the RFC 4193 algorithm (SHA-1 of an NTP timestamp and an EUI-64 derived from a MAC address). The output includes the /48, the chosen /64, its first and last addresses and a sample host address.
Common uses
- Pick a private IPv6 prefix for a home lab or internal network
- Plan /64 subnets inside a ULA /48
- Assign stable internal addresses that do not depend on the ISP prefix
- Address containers, VPNs or test environments over IPv6
FAQ
- What is an IPv6 ULA?
- A Unique Local Address is the IPv6 equivalent of private address space, defined in RFC 4193. ULAs are routable inside a site but not on the public internet.
- Why do ULAs start with fd and not fc?
- The ULA block is fc00::/7. The eighth bit (L) set to 1 gives fd00::/8, which is for locally assigned prefixes; fc00::/8 is reserved for a central allocation scheme that was never defined.
- Why should the Global ID be random?
- A random 40-bit Global ID makes it very unlikely that two networks pick the same prefix, which avoids conflicts if they are later connected by VPN or merged.
- How many subnets does a ULA /48 have?
- The 16-bit Subnet ID gives 65,536 /64 subnets, and each /64 has 2^64 interface addresses.