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Port scanning without permission is not very welcome, and it is even illegal in some countries. I recommend you to research your local laws to find out what you are permitted to do and if port scanning is frowned upon in your country. You also need to consult with your ISP as they may have their own rules on the subject.
The official documentation of Nmap has an amazing write-up about the legal issues involved with port scanning, available at https://nmap.org/book/legal-issues.html. I recommend that everyone considering doing Internet-wide research scanning reads it.
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