Learning DNS the Hard Way: When My Pi-hole Stopped Working (and My Internet Broke)

Hey fellow homelabbers and tech enthusiasts!

You know that feeling when everything in your network is humming along perfectly? Your dashboards are green, your services are running, and your Pi-hole is diligently blocking ads and tracking across your entire network. Pure bliss, right? Well, that was my world until a few months ago, when my perfect little digital bubble burst. My internet… just stopped working. Or so it seemed.

The Digital Silence: What Happened?

It was a typical evening. I sat down to browse, and suddenly, nothing loaded. No websites, no social media feeds, nothing. My first thought? Router. Always the router, right? A quick reboot. No change. Then, the modem. Still nothing. Panic started to set in. My wife was giving me 'the look' – the one that says, 'Honey, is the internet broken again?'

But here’s the kicker: I could still ping IP addresses. My local network devices were all communicating. I could SSH into my servers, access my NAS, even stream local media. It was only *external* services that were unreachable by name. That's when the little lightbulb (a very dim one at first) flickered: DNS.

The Frantic Flailing: Initial Troubleshooting

My initial troubleshooting steps were, to put it mildly, a bit chaotic. I was rebooting everything in sight, checking cables, verifying Wi-Fi connections – all the usual suspects. I even started to suspect my ISP was having an outage. But a quick check on my phone (on mobile data) showed the world was still spinning. This was definitely a *me* problem.

Eventually, I remembered that all my network clients were configured to use my Pi-hole as their primary DNS server. This was the linchpin of my network's ad-blocking and local DNS resolution. If Pi-hole was down, everything would stop resolving names.

Diving into the Pi-hole: Where the Real Learning Began

I SSHed into my Raspberry Pi running Pi-hole. A quick pihole status showed that the FTL (DNS resolver) service was running. The web interface was accessible. Everything seemed fine on the surface. But why wasn't anything resolving?

I tried a dig google.com directly from the Pi-hole's command line. No response. This was the critical clue! Pi-hole itself couldn't resolve external domains. This meant the problem wasn't that Pi-hole was down; it was that Pi-hole couldn't do its job because *its* upstream DNS was failing.

The DNS Chain: My 'Aha!' Moment

This is where my understanding of DNS truly deepened. I always knew DNS translated names to IPs, but I hadn't fully appreciated the *chain* of resolution:

Your device asks Pi-hole (its configured DNS server) for an IP address.Pi-hole checks its cache and local blocklists/whitelists.If not found, Pi-hole asks *its* configured upstream DNS server (e.g., Cloudflare, Google DNS) for the IP.The upstream DNS server then recursively queries other DNS servers (root, TLD, authoritative) until it finds the answer.The answer comes back through the chain to your device.

My problem was a broken link somewhere between step 3 and 4. Pi-hole was running, but it couldn't reach its upstream DNS provider, or that provider was having issues. In my case, I had configured Pi-hole to use a specific public DNS server that, unbeknownst to me, was experiencing intermittent outages.

The Fix and Lessons Learned

The fix was surprisingly simple once I understood the root cause: I went into Pi-hole's settings and changed its upstream DNS servers to a more reliable combination (Cloudflare and Google DNS, for redundancy). As soon as I applied the changes, the internet roared back to life.

This whole ordeal, while frustrating, was an invaluable learning experience. Here’s what I took away:

• DNS is the Foundation: Without working DNS, your internet is effectively broken, even if you have physical connectivity.

• Understand Your DNS Flow: Know exactly how DNS requests travel through your network, from client to Pi-hole to upstream.

• Monitor Your Pi-hole (and its Upstream): Don't just set it and forget it. Keep an eye on its health and make sure it can reach its upstream resolvers. Simple pings or `dig` commands from the Pi-hole itself can be lifesavers.

• Redundant Upstream DNS: Configure multiple reliable upstream DNS servers in Pi-hole to prevent a single point of failure.

• Check Logs: Pi-hole's logs and `pihole -d` are incredibly powerful debugging tools. I should have started there!

Now, I'm a bit more proactive. I've got some basic monitoring set up for my Pi-hole's upstream connectivity, and I regularly check its query logs. It's a small change, but it's given me a lot more peace of mind.

Have you had similar 'learning the hard way' moments in your homelab? Share your stories in the comments!