Re: dns lookup behavior

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On Mon, Feb 21, 2022 at 4:52 PM Barry <barry@xxxxxxxxxxxxxxxx> wrote:


> On 21 Feb 2022, at 20:15, Paolo Galtieri <pgaltieri@xxxxxxxxx> wrote:
>
> Folks,
>  I have 3 Linux systems, one running F31 and 2 running F34.  On one of the F34 systems I have a local DNS server running.  This has worked fine in the past, but now I'm seeing strangeness on the 2 F34 systems.
>
> I added a host to the DNS server for normal lookup and reverse lookup.  On the F31 system both:
>
> host centos8-opstcore-vm.homenet172-16-96.com
>
> and
>
> host 172.16.96.20
>
> work. The first returns 172.16.96.20 and the second returns centos8-opstcore-vm.homenet172-16-96.com.
>
> On the F34 which is the DNS server the first works, but the second fails with:
>
> Host 20.96.16.172.in-addr.arpa. not found: 3(NXDOMAIN)
>
> On the other F34 system I get:
>
> host 172.16.96.20
>
> ;; connection timed out; no servers could be reached
>
> The interface has the DNS server pointing to the correct system. If I run:
>
> nslookup
> > server 192.168.10.66
> Default server: 192.168.10.66
> Address: 192.168.10.66#53
> > 172.16.96.20
> 20.96.16.172.in-addr.arpa    name = centos8-opstcore-vm.homenet172-16-96.com.
> >

Nslookup has been replaced by the dig program.

Barry

>
> Then it works.
>
> What do I need to do on F34 systems to get DNS lookups working?

Might you be using systemd-resolved on the f34 to cache for you?
What does resolvectl report?

Barry

>
> Any help is appreciated.
>
> Paolo
>



In Fedora 33 DNS resolution was changed (1)adding a DNS server to /etc/resolv.conf using systemd-resolve.

There is still an /etc/resolv.conf and it is configured to use a name service running on a loopback device where a local DNS service is listening.

# grep -v '#' /etc/resolv.conf

nameserver 127.0.0.53
options edns0 trust-ad
search domain.com


If you are using the NetworkManager service just add the DNS server address and it should start working.

Something like this "nmcli con mod $connectionName ipv4.dns "1.1.1.1 9.9.9.9".


At first I didn't like this new way to manage DNS, but I am finding some of the features to work very well. Like the split dns feature is working really well with the multiple vpn clients run simultaneously, no more hacking on /etc/resolv.conf each time a new VPN is started, it just works.


1 - https://fedoraproject.org/wiki/Changes/systemd-resolved

 Regards,
-Jamie
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