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What to use as DHCP server? (lemmy.world)

submitted 1 year ago by [email protected] to c/[email protected]

30 comments fedilink hide all child comments

Hello everyone,

first time ever posting on lemmy, feels good 😉

I have a question regarding DHCP in my local network.

My current setup is as follows:

DHCP provided by router (Fritz!Box 7490)
DNS provided by pi-hole hosted on a raspberry pi
DHCP pushes the IP of the raspberry via DHCP to all clients

My problem is: When the raspberry pi (running pi hole) is down for any reason, none of my devices has internet access anymore. This is due to the fact that the Fritz!Box router (aka DHCP server) has no option to push a secondary DNS as a fallback to its clients.

One option would be to buy another router which has the option to push a secondary DNS, which I would prefer to avoid, since otherwise I am happy with the Fritz!Box.

So I am looking for alternative configurations with my existing hardware. I could for example use pi holes DHCP. Or I could use the DHCP server package of a synology NAS which is also part of my local network. Or is there another option, maybe using some DHCP service on the raspberry pi or in a docker container or something like that? Does anyone have experience with one of these setups and can tell me if it is possible to provide the clients with two (prioritized) DNS options? What would you recommend? Thanks!

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[–] [email protected] 9 points 1 year ago* (last edited 1 year ago) (8 children)

To me it sounds like you don't have a DHCP problem at all, the issue is no website can be resolved when your DNS is down (PiHole).

You really have two options:

Make sure the PiHole stays up 24/7, with minor downtime for maybe a reboot or an update.

Setup an additional raspberrypi with PiHole and use gravity-sync to keep them synced. Then, I would run ISC-DHCP server on both the raspberrypi's, one as the primary and the other as the secondary. That way you can specify both of your DNS servers. Make them authoritative and disable your routers DHCP. You can take a look at this guide:

https://stevendiver.com/2020/02/21/isc-dhcp-failover-configuration/

Personally, I like to keep the wife happy so I have option 2 at home, that way the internet never goes down when I tinker.

Edit: Didn't notice you said your router can't issue out two DNS servers. I've never heard of that.

[–] [email protected] 4 points 1 year ago (2 children)

Keepalived (or similar CARP or VRRP virtual IP system) would allow you to run 2 piholes that share the same virtual IP.
If the main goes down, the backup will take over the virtual IP

[–] [email protected] 3 points 1 year ago

Nice, but you don't need this per se. If you have two Piholes doing DNS, one of them can do DHCP and push the two pihole DNS server addresses. If the one with DHCP goes down temporarily you will not get a new addresses, but DNS resolution continues one the one running.

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