Cannot figure out DNS config

[Azhar]

My laptop is connected to home DSL which is configured with DHCP. From what i understand, DNS is also configured through DHCP.
I have a debian 12 system, in which i changed the resolv.conf to following

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# 
Generated by NetworkManager
nameserver 185.228.168.9
nameserver 8.8.8.8
nameserver 9.9.9.9

but when i run the following command it shows me DNS set by my DSL router

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( nmcli dev list || nmcli dev show ) 2>/dev/null | grep DNS

IP4.DNS[1]:                             192.168.10.1
IP4.DNS[2]:                             192.168.25.1

My question is, are the two IP4 DNS shown, are used by my system or network. If it is of my system, then why isn't it using DNS set in resolv.conf?


Edit

I got the following command through forums, i am not sure how it works or what it show

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( nmcli dev list || nmcli dev show ) 2>/dev/null | grep DNS

[Aki]

Hello,

I have a debian 12 system, in which i changed the resolv.conf to following

Code: Select all

#  Generated by NetworkManager
nameserver 185.228.168.9
nameserver 8.8.8.8
nameserver 9.9.9.9

but when i run the following command it shows me DNS set by my DSL router

Code: Select all

( nmcli dev list || nmcli dev show ) 2>/dev/null | grep DNS
IP4.DNS[1]:                             192.168.10.1
IP4.DNS[2]:                             192.168.25.1

My question is, are the two IP4 DNS shown, are used by my system or network. If it is of my system, then why isn't it using DNS set in resolv.conf?
Edit
I got the following command through forums, i am not sure how it works or what it show

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( nmcli dev list || nmcli dev show ) 2>/dev/null | grep DNS

The first line of /etc/resolv.conf shows the comment:

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#  Generated by NetworkManager

The NewtworkManager program will replace the contents of /etc/resolve.conf with the DNS server IP address received from the DHCP lease when it is used to configure the network using the DHCP service (this is the most common situation for home installations). So any IP manually added to /etc/resolv.conf beforehand can be removed after network configuration in this scenario.

You may investigate the output of the nmcli dev show command this way:

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script log.txt
getent ahosts 
PAGER= nmcli device show
exit

The file log.txt will contain the output of previous commands.

Here the manual page for nmcli:

• nmcli - command-line tool for controlling NetworkManager

Hope this helps.

[Aki]

Hello,
Did you sorted it out ?

[Uptorn]

The question of what program controls resolv.conf is a fun (as in ripping your hair out) rabbit hole explore.

It took me way too long to arrive at the conclusion that the most direct and DE-independent way to set one's preferred DNS resolvers is to do so through isc-dhcp-client while also making certain to disable competing programs that would otherwise attempt to overwrite resolv.conf (such as Network Manager, which you have installed).

First, I prevent Network Manager from interfering by editing /etc/NetworkManager/NetworkManager.conf

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[main]
dns=none

And then apply the changes

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sudo systemctl restart NetworkManager

Then I insert my preferred resolvers to /etc/dhcp/dhclient.conf

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supersede domain-name-servers 9.9.9.9;

*If you want to override the DNS servers provided by DHCP entirely and force the system to use the ones you provide, use the supersede entry:
supersede domain-name-servers

Then renegotiate DHCP

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sudo dhclient -r
sudo dhclient

This yields reliable, unchanging resolver entries at /etc/resolv.conf

I think a lot of old hats assume this is just obvious knowledge. But people that haven't been doing the whole *nix thing since the 90s are left to trial-by-fire.