How to split DNS resolution based on the target domain?

WoJ

5/14/23, 11:42 AM

Note: I read two other questions (here and here) that address the same problem but none of the solutions is applicable to my case.

I run Pi-hole in a docker container as my DNS server - for the server it is running on (Ubuntu 18.04), and the rest of my home network. It works fine, everything resolves as expected.

Except in one specific case: when Pi-hile itself is starting. It wants to check something on the Internet and fails because the DNS resolution obviously fails.

This is not the end of the world but this triggered my question: can I set up systemd-resolved so that it chooses a DNS server based on the requested domain?

The questions in my introductory note mention the ability to do a split DNS but my understanding is that the DNS can only be set on a per-NIC basis. In other words, for one interface there can be only one DNS (or several backup ones, what I mean is that there is no possibility of dynamically choosing the one to use).

Is this understanding correct?

0 + 0

networking

dns

display-resolution

systemd-resolved

matigo

5/14/23, 11:46 AM

Would it be feasible to have a custom entry for the domain in `/etc/hosts`? This would bypass the need for DNS for that one domain altogether, which may be alright so long as the target IP does not change

WoJ

5/14/23, 11:48 AM

@matigo: the problem with this solution is that I would need to list all the FQDN of the services, and this would need to be maintained manually. At some point I was considering writing a script to populate `/etc/hosts` with this information but I would very much prefer something more seamless.

muru

5/14/23, 11:52 AM

What happens if you write a custom `resolv.conf`, and mount that inside the Pi-Hole container at `/etc/resolv.conf`?

WoJ

5/14/23, 12:02 PM

@muru: so that the name that fails during startup is forcefully resolved, you mean? Yes, that's an idea but the target IP can change. Still, it is a fix and I would check from time to time if this manual resolution is still fine. Thanks for the hint (I guess that my understanding of how dynamic/split DNS works is (unfortunately to me) correct, right?)

muru

5/14/23, 1:06 PM

`resolv.conf` contains DNS configuration (like nameservers, search domains, etc.). So essentially you're just setting up a separate DNS configuration for Pi Hole, that's all - not hardcoding IPs for some domains - that's `/etc/hosts`.

WoJ

5/14/23, 1:11 PM

@muru: ahhh, sorry, I read `/etc/hosts` instead of `/etc/resolv.conf` ! Ah yes, this is now a very good idea :) Thanks, I will try it right away!

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: How to split DNS resolution based on the target domain?

TH: จะแยกความละเอียด DNS ตามโดเมนเป้าหมายได้อย่างไร

RO: Cum să împărțiți rezoluția DNS în funcție de domeniul țintă?

RU: Как разделить разрешение DNS на основе целевого домена?

VI: Làm cách nào để phân chia độ phân giải DNS dựa trên miền mục tiêu?

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