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Networking Fundamentals · Intermediate

Unique Local Address (ULA)

IPv6 addresses in fc00::/7 (in practice fd00::/8) meant for local use within a site or group of sites, similar to IPv4 private addresses.

Definition

ULAs (RFC 4193) use a 40-bit pseudo-random global ID to make collisions unlikely if networks merge. They are routable within an organization but not on the Internet. Their use alongside global addresses is optional.

Example

fd12:3456:789a:1::10/64 is a unique local address.

Exam tip

ULA (fd00::/8) is the IPv6 counterpart to RFC 1918; the deprecated site-local range fec0::/10 is not used.

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