Use domains and IPs specified by the respective RFCs: RFC-5737 for IPv4, RFC-3849 for IPv6, and RFC-2606 for domains
Specifically, those are:
203.0.113.0/24
for example public IPv4 addresses198.51.100.0/24
for example private IPv4 addresses2001:DB8::/32
for example IPv6 addressesexample.com
, example.net
, example.org
, or example.edu
for domains