>APNIC's research group held the IP addresses 1.1.1.1 and 1.0.0.1. While the addresses were valid, so many people had entered them into various random systems that they were continuously overwhelmed by a flood of garbage traffic. APNIC wanted to study this garbage traffic but any time they'd tried to announce the IPs, the flood would overwhelm any conventional network.

>We talked to the APNIC team about how we wanted to create a privacy-first, extremely fast DNS system. They thought it was a laudable goal. We offered Cloudflare's network to receive and study the garbage traffic in exchange for being able to offer a DNS resolver on the memorable IPs. And, with that, 1.1.1.1 was born.[0]

[0]https://blog.cloudflare.com/announcing-1111/

It's not a reserved address like 192.168.0.0/16 or 10.0.0.0/8[1][2], nor is it one of the other reserved addresses for documentation or testing. So I think people using it before as test or LAN addresses are actually in the wrong here. This kind of "tradition" in networking is wrong. That's what things like RFC's are for.

[1]https://tools.ietf.org/html/rfc5735

[2]https://www.iana.org/assignments/iana-ipv4-special-registry/...