Nope. Ports that you can use are already advertised to you: web links, MX records, registrar records, WSDLs etc. Enumerating all ports that aren’t advertised to

Nope. Ports that you can use are already advertised to you: web links, MX records, registrar records, WSDLs etc. Enumerating all ports that aren’t advertised to you is an overreach.