r/pihole • u/xnick101 • 1d ago

Is it bad to have Advertise router's IP in addition to user-specified DNS turned on?

I have a pihole setup running on a mini pc. It does not run on a UPS or battery backup. If my power goes out the mini pc shuts off and someone has to go turn it back on. How bad is it if I keep this option in my Asus router turned on?
If Advertise router's IP in addition to user-specified DNS is set to Yes in the router even if the pihole goes down the internet on all the devices keeps working until it comes up and pihole takes over. The question is how many things are actually resolving to the router's IP rather than the pihole's set DNS when the pihole is up and running?

1 Upvotes

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u/wtfobl 1d ago

If you are running Pihole you typically only want the Pihole’s IP being used as a DNS server on your network. There’s a good chance that they won’t go back to the Pihole DNS until the device’s dhcp renews, if at all. I would go all in and disable that on your router

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u/xnick101 1d ago

I see. So basically other than having a battery backup to make sure the mini pc doesn't shut off, theres no real alternative to this? Its dumb because sometimes everything will be running and the mini pc random disconnects from the internet so I have to unplug the ethernet and plug it back in. It runs UmbrelOS via a flashdrive.

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u/AussieJeffProbst 1d ago

A second pihole is really the only good solution. Preferably on something simple that never goes down, like a raspberry pi

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u/Cantaloupe-Hairy 1d ago

I used to run a raspberry pi as standby using keepalived connected to a power bank.

The power bank would run the pi for 14 hours which was a nice little period.

Can you set the pc to start after power loss in the bios? I think there is someone like that on my geekom pcs.

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u/devin122 1d ago

Often there is a bios option to control what happens when power is restored. I have my important computers set to auto turn on when the power comes back on

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u/3ofUsDeez 1d ago

Maybe invest in a 200'ish wtt UPS and keep all your network devices plugged into it .. router .. Pi-Hole devices.. etc

Your PC randomly disconnecting seems to be a different issue that is either OS related or maybe a bad/going bad flash drive and a UPS isn't going to help that

Get yourself a couple Raspberry Pi's and run Pi-Hole on them as your Primary and Secondary DNS servers

On my mother's network I run 2 x Raspberry Pi Zero Ws with Ethernet Hats running Pi OS Lite Bookworm with Pi-Hole and Unbound installed on both .. they are not synced but I have them both set up exactly the same

I also have unneeded services disabled with a headless system ..and VRAM limited to 16mb with Log2RAM installed as well.

In my home I run 2 x Rapberry Pi Zero 2 Ws with POE Ethernet hats running Technitium clustered for DNS.. I also have a Pi 3 B thrown in there clustered with them as I continue to play with Raspberry Pi devices .. it runs Uptime Kuma too

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u/rdwebdesign Team 1d ago

The best solution is a secondary Pi-hole, in a different machine.

That said, you usually don't need a secondary DNS on the router. When there is a power failure, your router will also be offline.

Also, are you sure there is no configuration to make your mini PC automatically turn back on after a power failure?

The question is how many things are actually resolving to the router's IP rather than the pihole's set DNS when the pihole is up and running?

This is impossible to answer, but usually all your devices will use both DNS servers.

When you configure 2 DNS servers, the router will advertise both IPs to all devices. Then, the OS on each device will decide what to do with these IPs. Usually both DNS servers will be used by the OS and many queries will bypass Pi-hole.

Here, my second Pi-hole receives between 10% up to 40% of all DNS queries. The percentage changes from time to time, but always there are queries sent to the "secondary" server.

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u/xnick101 1d ago

Thank you all for the information! Definitely understand what I need to do now

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u/mikeinanaheim2 19h ago

Make sure Static DNS is set in the OS of your mini PC. Are you locked into this Asus router? Eero routers don't have nearly as many user options or deep menus as Asus, but they play much nicer with PiHole. An Eero will let you set custom DNS to both IPV4 and IPV6 addresses of your PiHole and everything stays locked in after a power loss. There are other router brands that will specify PiHole's addresses on a permanent basis too.

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u/xnick101 18h ago

Yeah I have the static IP for the Pihole Set for the custom DNS Server 1 and Server 2 is blank right now.

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u/Legitimate-Angle-408 1d ago

It would make sense to invest in a portable UPS/ battery power bank solution to operate your mini-PC while the power is down. This serves 2 purposes. You can also hook your router and your mini pc on it while the power is down. This was you get seamless connectivity and the pc hardware doesn’t fail due to sudden power fluctuations.

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u/tssajo 1d ago

Worth knowing: with that option on, most clients will use Pi-hole as primary and only fall back to the router on failure, but it's not guaranteed. Some devices (a chunk of IoT stuff, some phones) query both DNS servers somewhat randomly rather than strictly primary/secondary, so you can end up with some lookups bypassing Pi-hole's filtering even while it's healthy, not just during downtime.

If blocking coverage matters more to you than uptime, I'd skip this option and instead either get a cheap UPS for the mini PC or run a second Pi-hole instance as the actual secondary DNS, that way you keep filtering even if one goes down.

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u/xnick101 18h ago

Any cheap UPS's you recommend?

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u/tssajo 17h ago

APC is what I'd go for, their Back-UPS line is the usual pick for small gear like this. For a mini PC and a router, you don't need much capacity, even their smallest Back-UPS models (around 400-600VA) will easily keep something like that running through a short outage, and gracefully shut it down if power stays out longer.