As a way to avoid this problem, the IETF published Best Current Practice (BCP) 32 in 1999. BCP 32, also known as RFC 2606, defines four reserved TLDs — .test, .example, .invalid, and .localhost ... that are guaranteed never to be assigned so that researchers and developers can always use them for example and testing purposes without concern. ↑ "IANA — Root Zone Database". www.iana.org. Retrieved 2022-05-07. ↑ "IANA-managed Reserved Domains".