Using ISP DNS

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1

Hi. I'm new to Pi-hole, and still learning DNS, but enjoying things thusfar.

I guess the meat of my question is: how do I set Pi-hole to use my ISP's DNS resolver? (as opposed to eg. Cloudfare, Quad9, etc)

I have Pi-hole running on an armhf device with Ubuntu 22.04, and a Linksys router connected to it, and have successfully used Pi-hole with eg. Cloudfare from my networked devices, but I'd like to use my ISP's DNS server instead, and mainly use Pi-hole just for its filtering and logging.

The main problem I think I have is: I don't know how to determine the IP address of my ISP's DNS server. I've run dig +trace example.com and similar, though the servers included in the output only consist of 192.168.1.1#53 (my router) and the root/gtld/iana/... nameservers you would expect for such a query.
(I've run that command when Pi-hole has effectively been "disabled"--with my router not forwarding DNS requests to Pi-hole--expecting to see an IP address for my ISP's DNS server somewhere in there.)

One other wrench I suspect I need to consider is: I think it's possible that the IP address of my ISP's DNS server may change (at least in theory), so I'm not sure how to best handle that.

I'm open to eg. running more commands to figure things out.

Thanks in advance for your wisdom!

2

Your ISP may list their DNS server IP's on their support page, or you can call them and ask.

3

It should also show up in the router settings as the router's upstream DNS, if you didn't replace this with the local Pi-hole IP.

4

You could also consider the following setup: Just let your router use your ISP's DNS servers (as it did before using Pi-hole) and configure your router's DHCP server to broadcast your Pi-hole as DNS server. This will ensure your local devices will all use the Pi-hole. Then configure your router as the sole upstream server in Pi-hole and let your router forward the queries to wherever it deems appropriate. In theory, this should be to the ISP DNS servers.

If your Linksys router cannot be configured for this, you could consider switching off the router's DHCP server and simply use Pi-hole's one. It is automatically configured to broadcast your Pi-hole as DNS server. Note that your devices will not be informed when switching the DHCP server, you either have to wait until the current leases expires (can take several days up to a month depending on the Linksys configuration) or force a refresh by pulling the Ethernet cable or even restart the entire device.

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