How does DNS work for the ISP?

I started a blog tonight on DNS design for the ISP. As a result of this writing, I found myself explaining a lot of what the following video does. So if you are not familiar with how DNS works please watch the following video and look for a new post soon on DNS design for the ISP.

j2networks family of sites
https://j2sw.com
https://startawisp.info
https://indycolo.net