A reference for placeholder data. These are data that are designed to be used in tests or examples, which are "obviously invalid" or do not work in production scenarios.
RFC2606 guarantees that the following TLDs will not be registered:
.example: for use in documentation or examples.test: for use in tests.invalid: catch-all invalid TLD
.localhost is also guaranteed to never be registered.
RFC 5737 reserves the following IPv4 blocks for test or documentation purposes:
192.0.2.0/24("TEST-NET-1")198.51.100.0/24("TEST-NET-2")203.0.113.0/24("TEST-NET-3")
RFC 3849 reserves the following IPv6 block for test or documentation purposes:
2001:db8::/32