::/128: Unspecified Address address range

::/128

Last updated 2 Nov 2026 from the IANA IPv6 Special-Purpose Address Registry

Short answer

:: is the IPv6 unspecified address: “no address yet”.

Block	::/128
First – last	:: – ::
Size	a /128 (2^0 addresses)
Name in the registry	Unspecified Address
Defined in	RFC 4291
Allocated	2006-02
Valid as source / destination	True / False
Forwardable	False
Globally reachable	False

What it means

RFC 4291 defines :: (all zeros) as the unspecified address. A device uses it as a source address while it is still getting a real one; software also uses it to mean “listen on every interface”.

It never appears as a real destination.

Want the address websites actually see for you? Open the Truth Check.

Sources

IANA IPv6 Special-Purpose Address Registry (CC0) · checked 2 Nov 2026
RFC 4291