https://www.nslookup.io/dns-course/

I've had many side projects over the years, and never completely understood why my DNS records didn't update. Or how long to wait until they do. Worse yet, I've had my emails bounce because I misconfigured SPF, DKIM and DMARC.  I decided to learn DNS by making Nslookup.io, a web interface for DNS. I've read the RFCs to implement a custom DNS client and I now run my own DNS server. Nslookup has become popular enough to replace my income, so I'm working on it full-time since early 2022.  Now that I've spent so much time learning DNS, I'm sharing everything I've learned in this comprehensive video course. It will teach you to reason about DNS from first principles and guard you against the mistakes I made. When you finish this course, you will be able to manage and debug DNS with confidence.