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A custom port for DNS (self.archlinux)

submitted 2 weeks ago by Reza to c/[email protected]

9 comments fedilink hide all child comments

I want to set the system to send DNS queries with a custom port, not 53. I added DNS=127.0.0.1 9053 to /etc/systemd/resolved.conf and DNS=127.0.0.1:9053 to /etc/systemd/networkd.conf. But now DNS queries are sent via the default DNS with port 53. What can I do?

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

I ran the command with sudo and got the error.

Yes, that's why I said don't do that. It's a common, non-intuitive interaction with sudo and shell redirections. Don't stress over it, I shouldn't have done it all that fancy in the first place.

Regarding your problem: Your setup is likely inconsistent now due to your experiments and previous setup attempts. HOLD THE REINSTALL, learn to fix it, it's not that complex. First off: you're not running in the recommended "stub mode" where /etc/resolv.conf is symlinked to /run/systemd/resolve/stub-resolv.conf, and where the configuration you did is actually actively used. Fix that first. Have some docs. This is my stub /etc/resolv.conf, for example, so you know what to look for, roughly:

[root@e15g4 gyroplast]# cat /etc/resolv.conf 
# This is /run/systemd/resolve/stub-resolv.conf managed by man:systemd-resolved(8).
# [...]
nameserver 127.0.0.53
options edns0 trust-ad
search fritz.box

Don't create that file with these contents manually. Read the docs, follow the instructions, don't ruin your day.

Assert you have no lingering, conflicting setup in the /etc/systemd/resolved.conf main config. The default file is effectively empty / commented out, to allow for automatic system updates without conflicts. You could reinstall the package to get the original file back if you're unsure.

Make sure the systemd-resolved.service is enabled and started: systemctl enable --now systemd-resolved.service You might want to install systemd-resolvconf as well if you commit to a systemd-resolved setup, for maximum compatibility.

Make use of resolvectl status to verify the status:

Global
           Protocols: +LLMNR +mDNS -DNSOverTLS DNSSEC=no/unsupported
    resolv.conf mode: stub
  Current DNS Server: 127.0.0.1:9053
         DNS Servers: 127.0.0.1:9053
Fallback DNS Servers: 1.1.1.1#cloudflare-dns.com 9.9.9.9#dns.quad9.net 8.8.8.8#dns.google
                      2606:4700:4700::1111#cloudflare-dns.com 2620:fe::9#dns.quad9.net 2001:4860:4860::8888#dns.google
[...]

If that's still not what is expected, crank up debugging and check the logs of the service to see if for some reason your config file isn't loaded due to a typo somewhere, or if it's loaded, any other reason that may override your settings later. It's practically guaranteed there's an inconsistency left somewhere, and reading the debug log points you at the actual problem.

It's worth fixing this in that way. With stub mode, you gain a lot of flexibility in your setup, and it works well in tandem with NetworkManager, DHCP, VPNs, and libvirt/qemu networking. You have to make sure you're not inadvertently setting up some broken "hybrid" of old-school /etc/resolv.conf manual config and systemd-resolved, this will drive you mad, and it's a pain to diagnose. Read that wiki page, do not intermingle with crap you pick up on stackoverflow or AI bullshit, and you'll end up with a DNS config that actually works like magic.

[–] Reza 1 points 2 weeks ago (3 children)

Thank you for spending your time. Yes, resolvectl status's output is like yours in Global part, but in the end of the output there is this:

Link 3 (wlp3s0)
    Current Scopes: DNS LLMNR/IPv4 LLMNR/IPv6 mDNS/IPv4 mDNS/IPv6
         Protocols: +DefaultRoute +LLMNR +mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 192.168.1.1
       DNS Servers: 192.168.1.1
     Default Route: yes

As you see, wlp3s0 uses the default ISP DNS. Wireshark's output confirms this.

[–] [email protected] 3 points 2 weeks ago (2 children)

Yeah, that's normal, intended, and does not prevent general lookups taking the global DNS first. Do you see an issue with this?

I gave this setup a try real quick, to make sure I'm not overlooking something, with dnsmasq for testing on 127.0.0.1:9053:

[gyroplast@e15g4 ~]$ dnsmasq --listen-address=127.0.0.1 --port=9053 --address=/testme.localnet/127.42.0.69 --no-daemon --no-hosts --no-poll --log-queries
dnsmasq: started, version 2.90 cachesize 150
dnsmasq: compile time options: IPv6 GNU-getopt DBus no-UBus i18n IDN2 DHCP DHCPv6 no-Lua TFTP conntrack ipset nftset auth cryptohash DNSSEC loop-detect inotify dumpfile
dnsmasq: warning: no upstream servers configured
dnsmasq: cleared cache

When triggering a query on that test record, f. ex. with ping -c1 testme.localnet, you'll see it's directed to the dnsmasq instance and working as intended:

dnsmasq: query[A] testme.localnet from 127.0.0.1
dnsmasq: config testme.localnet is 127.42.0.69
dnsmasq: query[AAAA] testme.localnet from 127.0.0.1
dnsmasq: config error is REFUSED (EDE: not ready)
dnsmasq: query[AAAA] testme.localnet from 127.0.0.1
dnsmasq: config error is REFUSED (EDE: not ready)

The DNS setup with systemd-resolved is pretty confusing, and outright contradicts many, MANY previously correct instructions of how to set your /etc/resolv.conf. I'm not surprised if it is giving you a headache right now, but all I can say is to diligently work through its configuration, and understand how systemd-resolved is supposed to work. From experience, make sure your tests are sound and representative, or you'll continue looking for errors in your setup despite everything actually working just fine, maybe because you missed a reload or had a typo or misunderstanding in your wireshark filter.

In the same vein, make sure your DNS listening on :9053 is really working as intended, otherwise you can bark up the wrong tree all day long. Debug logging is your friend, and more accessible and less error prone than tcpdump/wireshark.

You'll figure it out from here, I'm sure.

[–] Reza 1 points 2 weeks ago (1 children)

Thanks! I wasted your time. As you said the problem caused a headache to me. I stop trying on it for some days.

[–] [email protected] 2 points 2 weeks ago

Wise decision! Best of luck for when you give it another try, with fresh eyes and a clear mind, and enjoy your XP gain dopamine on the way.