192.88.99.0/24

192.88.99.0/24 was the 6to4 relay anycast range; RFC 7526 deprecated it.

Last updated 2 Nov 2026 from the IANA IPv4 Special-Purpose Address Registry

Short answer

Block	192.88.99.0/24
First – last	192.88.99.0 – 192.88.99.255
Size	256 addresses
Name in the registry	Deprecated (6to4 Relay Anycast)
Defined in	RFC 7526
Allocated	2001-06
Valid as source / destination	— / —
Forwardable	—
Globally reachable	—

What it means

6to4 let IPv4-only networks reach IPv6 through public relays at 192.88.99.1. It caused enough reliability problems that RFC 7526 deprecated the relay anycast prefix in 2015.

Modern systems should not send traffic here.

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Sources

IANA IPv4 Special-Purpose Address Registry (CC0) · checked 2 Nov 2026
RFC 7526