On Thu, Feb 18, 2021 at 10:39 am, David Both <LinuxGeek46@xxxxxxxx>
wrote:
Ok, so I manage my network using DHCP on an internal server for all
except that server and my Linux firewall/router which both use a
complete static configuration for networking.
My DHCP server does provide DNS resolver information which, in order,
is my internal BIND server (same physical server host), 8.8.8.8, and
8.8.4.4. But my hosts were not getting that information. I think the
difference between the working and failing hosts is possibly
(experiments required) left-over ifcfg files some of which specified
DHCP but also name servers while others specified DHCP but did not
specify name servers, as well as some newer hosts that do not have
any ifcfg files. I have also noticed that ifcfg files are no longer
created automatically but work when created. I missed that
information also.
OK, so DHCP is not working somehow. Are you running NetworkManager?
That is my #1 guess right now, because without NetworkManager, you have
no easy way to get DNS configuration from DHCP to systemd-resolved.
systemd-resolved doesn't configure itself: that's the responsibility of
a higher-level management layer, usually NetworkManager, or
alternatively systemd-networkd. You can configure it manually with your
own scripts if you're really hardcore. But if you have disabled
NetworkManager, then my recommendation would be to disable
systemd-resolved as well. If you *are* running NetworkManager, then
unfortunately we're probably going to need to debug NetworkManager to
figure out why the configuration from DHCP is getting dropped. I don't
know how to help with that, but that also seems unlikely because nobody
has reported bugs related to that as far as I know.
If you are running NetworkManager, here are some more general
troubleshooting steps that I had typed up to send before reading the
above:
The most important thing to do is to check the output of 'resolvectl'
and look for anything suspicious. Ideally the DNS server you want
things going to will be listed under each desired network interface
with +DefaultRoute set. Hopefully something will be obviously wrong
there, but if not, you can post the output of 'resolvectl' here for us
to take a look.
To ensure systemd-resolved's configuration doesn't get bypassed, you'll
also want to ensure you're running Fedora's new default configuration,
which you should be, since users should be automatically upgraded. But
just in case, it's good to check:
* Ensure NetworkManager is running ('systemctl status
NetworkManager.service'). If not, you're on your own and should
consider disabling systemd-resolved since it's not worth trying to use
manually.
* Ensure systemd-resolved is running: 'systemctl status
systemd-resolved.service'
* Ensure /etc/resolv.conf is symlinked to
/run/systemd/resolve/stub-resolv.conf (this ensures anything reading it
manually gets pointed to systemd-resolved's IP address, 127.0.0.53)
* Ensure the hosts line in /etc/nsswitch.conf looks like this: files
mdns4_minimal [NOTFOUND=return] resolve [!UNAVAIL=return] myhostname dns
(Remember to never edit /etc/nsswitch.conf manually, instead edit
/etc/authselect/user-nsswitch.conf and then run 'sudo authselect
apply-changes'.)
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