-Unencrypted DNS requests are able to be easily **surveilled** and **modified** in transit. In some parts of the world, ISPs are ordered to do primitive [DNS filtering](https://en.wikipedia.org/wiki/DNS_blocking). When you request the IP address of a domain that is blocked, the server may not respond or may respond with a different IP address. As the DNS protocol is not encrypted, the ISP (or any network operator) can use [DPI](https://en.wikipedia.org/wiki/Deep_packet_inspection) to monitor requests. ISPs can also block requests based on common characteristics, regardless of which DNS server is used. Unencrypted DNS always uses [port](https://en.wikipedia.org/wiki/Port_(computer_networking)) 53 and always uses UDP.
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