I've found that teaching DNS is an excellent gateway to learning about how the internet itself works, especially to "green" tech folks who go blank-faced when you get into protocols, IPs, etc.

Break out a piece of mail, connect the dots, and you see their eyes light up with comprehension. "Oh, so that's how my computer gets to google.com; it's just like how my postman knows where to deliver my mail!" Then a critical component is demystified, and they want to learn more.

Running a DNS server is honestly such a good activity for folks in general.