DNS Problem "Temporary failure in name resolution"

Icinga 2
1

I have a VM with a new installation of Ubuntu 24.04. Set up static IP editing the yaml file:

    network:
      version: 2
      renderer: networkd
      ethernets:
        ens192:
          dhcp4: false
          addresses:
            - 10.32.8.49/24
          routes:
            - to: default
              via: 10.32.8.1
          nameservers:
             addresses: [10.32.8.60, 10.32.8.76]

The networking works ok, I can connect to the box, but DNS keeps failing and giving the “Temporary failure in name resolution” error.

I’m confused as to whether netplan even uses the /etc/resolv.conf file, but I’ve also edited that and manually inputed the nameservers, as it started off with just a listing for 127.0.0.53.
I’ve edited the file and put in the name servers there too, but I still get an error when trying to ping a local server or Google. But after editing the resolv.conf file, the error changes to “Name or service not known”.

I have no idea what’s going wrong. I’m more of a Windows guy than Linux, but this is our Icinga2 server.

Another question: Is there something actually wrong? The only thing that fails are pings… everything else works. I can SSH from the server without a problem, I can run ‘apt-get update’ and it works without a problem.
If the only thing that fails are pings, is that a bad thing? Will that affect my Icinga2 server?

2

Hi @TowerMark,
I am not an expert in netplan, but I
might be able to help.
netplan might make use of /etc/resolv.conf but by adding a local resolver
(probably systemd-resolved).
You can test this by using the command resolvectl which is an interface to systemd-resolved,
it should display your resolve (DNS) configuration.
You should be able to find the two DNS servers ( 10.32.8.60, 10.32.8.76) there.
If that is the case, you can test DNS resolution with the host command (host google.de) or the dig command (dig google.de).

As to your question whether this aggravate the working of Icinga, the answer is “it depends” and it depends on whether and how you need name resolution.
I tend to add Hosts with the address directly to avoid being dependent on working DNS, but it is just a choice.

3

Thank you. I’ve tried resolvectl before and it returns the appropriate DNS servers. I can also use the ‘host’ command you mentioned and it works as well, returning all appropriate information, so maybe it’s just that pings are blocked, so there’s not actually a problem. All my apt-update’s and get’s have worked as well, so there doesn’t seem to be a DNS or networking problem.

4

But pings still fail with the name resolution error?

5

Yes. But ‘host’ works. And all apt updates, etc. work jut fine.

6

FYI, some admins like to firewall-away ping. (“security feature”)

1 Like
7

But then it shouldn’t be name resolution error.

1 Like
8

To bisect this: For which names does name resolution fail?

9

Both, kinda.
Internal sites get “Temporary failure in name resolution”.
External sites frequently hang trying.

10

ok, this is weird. Are there any problems with your DNS server (that you know of)?
Maybe there is something in the logs there, rejected queries or such things.