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100:0:0:1::/64

100:0:0:1::/64 is the Dummy IPv6 Prefix block.

Last updated 26 Oct 2026 from the IANA IPv6 Special-Purpose Address Registry

Short answer

IANA lists 100:0:0:1::/64 as “Dummy IPv6 Prefix” (RFC 9780). It is not an ordinary public address.

Block100:0:0:1::/64
First – last100:0:0:1:: – 100::1:ffff:ffff:ffff:ffff
Sizea /64 (2^64 addresses)
Name in the registryDummy IPv6 Prefix
Defined inRFC 9780
Allocated2025-04
Valid as source / destinationTrue / False
ForwardableFalse
Globally reachableFalse

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Sources

  1. IANA IPv6 Special-Purpose Address Registry (CC0) · checked 26 Oct 2026
  2. RFC 9780