All-digit host names have been allowed since 1989. https://tools.ietf.org/html/rfc1123#page-13 https://tools.ietf.org/html/rfc1123#page-13 One aspect of host

All-digit host names have been allowed since 1989. https://tools.ietf.org/html/rfc1123#page-13 https://tools.ietf.org/html/rfc1123#page-13 One aspect of host name syntax is hereby changed: the restriction on the first character is relaxed to allow either a letter or a digit. Host software MUST support this more liberal syntax.