Yes, indeed, it is difficult to find information about DNS on the Internet. But recently a friend recommended this site to me https://technologeek.net/free-netflix-dns-codes-for-us-2021/ . It describes in detail what DNS codes are and how to use them. The site is informative and useful, I recommend that you visit it because such information is very little on the Internet and it is very difficult to find. I think you will now be more aware of what DNS codes are.