Blocking ads before they enter your house at the DNS level with pi-hole and a cheap Raspberry Pi

Lots of folks ask me about Raspberry Pis. How many I have, what I use them for. At last count there's at least 22 Raspberry Pis in use in our house. A Pi-hole is a Raspbery Pi appliance that takes the form of an DNS blocker at the network level. You image a Pi, set up your network to use that Pi as a DNS server and maybe white-list a few sites when things don't work.