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::1/128

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

Short answer

::1 is the IPv6 loopback address: it always means “this same device”.

Block::1/128
First – last::1 – ::1
Sizea /128 (2^0 addresses)
Name in the registryLoopback Address
Defined inRFC 4291
Allocated2006-02
Valid as source / destinationFalse / False
ForwardableFalse
Globally reachableFalse

What it means

RFC 4291 defines ::1 as loopback, the IPv6 equivalent of 127.0.0.1. Traffic to it never leaves the machine.

It cannot identify anyone else.

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Sources

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