Ads? What Ads?

Written by: Mike Helmers

For the last month or so there has been a noticeable decrease in the number of ads appearing on our network. Why? I installed a Pi-hole.

Using the same Raspberry Pi Zero from my OpenVPN project, I installed a program called Pi-hole. This nifty piece of software shuttles ad requests into a black hole. It works by acting as a DNS server, identifying ad domains before they download, and dropping them.

What is DNS?

DNS stands for Domain Name System. From Sideways Dictionary:

"It's like a contact list on your mobile phone. You know your correspondents by their names but the contact list has telephone numbers and postal addresses. When you want to go to a particular website, you look up the site's name in the Domain Name lookup service and get back the Internet Protocol address of the destination."

Pi-hole maintains a list of millions of known ad domains. Whenever a request for one of those addresses comes through, it throws it away.

Steps to Follow

Install Pi-hole
Configure DNS settings on my router
Update OpenVPN settings to route through Pi-hole

1. Install Pi-hole

Incredibly simple. One command:

curl -sSL https://install.pi-hole.net | bash

The script walks you through a few questions and then you're done. That's really it.

2. Configure DNS on the Router

Log into your router by entering its local IP address in a browser (usually 192.168.1.1). Navigate to the DHCP settings and set a static DNS pointing to your Pi's local IP address — in my case, 192.168.1.104. This routes all network DNS traffic through the Pi, stripping ads before they load.

3. Update OpenVPN to Use Pi-hole

OpenVPN defaults to using 8.8.8.8 (Google's DNS). I wanted to change that to my Pi-hole so VPN traffic also gets filtered.

Edit the OpenVPN server config:

sudo nano /etc/openvpn/server.conf

Update the dhcp-option DNS line to point to your Pi-hole's IP address.

Then create a new file in the dnsmasq config directory:

sudo nano /etc/dnsmasq.d/00-openvpn.conf

Add the following line:

interface=tun0

This is the important part. By default, Pi-hole only listens on the eth0 interface (ethernet). The tun0 interface is the VPN's virtual tunnel. This file tells Pi-hole to also filter traffic coming through the VPN.

Why bother for the phone? Blocking ads while on cellular can save real data — potentially quite a few MB per month.

The Admin Interface

Pi-hole includes a web dashboard accessible from any browser on your local network. In my case: http://192.168.1.104/admin. From there you can view traffic stats, tweak the whitelist and blacklist, and watch the DNS requests roll in.

It's satisfying to watch the stats — you can clearly see the flat network activity while we sleep, and the spike when we pick up our phones in the morning.

Takeaways and Future Thoughts

Unexpected problems: Port 80. Pi-hole creates a small web server on port 80 for the admin console and for redirecting blocked requests. When I tried to set up a separate web server on the same Pi, it wouldn't work — Pi-hole had already claimed the port. For anything public-facing, HTTPS (port 443) is the right choice anyway, so this isn't a huge constraint.

Future concerns: Port 80 is unavailable for other uses on this Pi. For now that's fine.

Future enhancements: Use Pi-hole to monitor traffic and look for unusual spikes in DNS requests — a potential early indicator of malware or bots on the network.