I thought this is basic knowledge of everyone technically engaged in Internet stuff. But apparently, this isn't the case, despite its well-known and very readable documentation! [1] It says: 1) There are exactly 3 domains the IANA keeps free for that purpose: example.com example.net example.org 2) In addition, all domains under the following 3 top level domains can be used freely for that purpose: *.test *.example *.…
IPv4: 192.0.2.0/24 - as described in RFC3330, http://www.faqs.org/rfcs/rfc3330.html
IPv6: 2001:db8::/32 - as described in RFC3849, http://www.faqs.org/rfcs/rfc3849.html