Domain names not properly resolved in Ubuntu 24.04 although Forticlient VPN is running

[ceperic]

I installed Forticlient VPN 7.4.3 without troubles. The connection looks fine and I get access to the intranet of my company when I use the exact IP number, but I cannot use names. I get the error DNS_PROBE_FINISHED_NXDOMAIN.

I checked the nslookup resolves the webnames.

I checked that quetying resolvectl does not work, but applying the solution posted in https://community.fortinet.com/t5/Support-Forum/Ubuntu-24-04-Forticlient-VPN-installation-w-DNS-reso..., makes it work.

Even though, I still get DNS_PROBE_FINISHED_NXDOMAIN in the navigator.

I am absolutely lost right now.
Any idea of what may be going on?

Thank you!

[AEK]

Hi

If nslookup works then it is basically working.

In that case if you get DNS_PROBE_FINISHED_NXDOMAIN error in your browser then probably the browser is not using the system DNS configuration. This may happen if your browser uses DNS security, like DNS over HTTPS with cloudflare or google and so.

Try go to browser settings > DNS, then disable DNS security and try again.

[ceperic]

Hi, thank you for answering.

I've tried everything, disabling secure DNS, cleaning DNS cache, flags, ...

I tried with different browsers, reinstalled them, tried again, ... and nothing.

[funkylicious]

hi,

when you are trying to access the webpage, do you use the full FQDN like intranet.mycompany.com or just intranet ?

also, doing a nslookup for just the hostname and not the FQDN works ?

[ceperic]

Hi,

I'm doing it with the FQDN, with just the hostname doesn't work.

[funkylicious]

have you tried with a different browser ?

also, a curl or telnet on the fqdn is working ?

[ceperic]

I've tried and failed.

But I got some useful output.

I modified /etc/systemd/resolved.conf putting in the DNS list the DNS address of the VPN in first (or second) position, restart systemd-resolved.service and worked.

Thank you for the help!

[ceperic · Accepted solution]

I found a solution, maybe was a trivial mistake from my side, but just in case is useful for someone I will put it here.

What I did is to modify resolved.conf to force the VPN-DNS to be first or second, i.e.

sudo nano /etc/systemd/resolved.conf

Uncomment the line "DNS=", and add the list of DNS putting the first or second, e.g. DNS=VPN-DNS 8.8.8.8 10.1.1.4

Then restart with: sudo systemctl restart systemd-resolved.service

If after this the browser still doesn't work,but nslookup works, then you need to link the resolv.conf, for that:

sudo mv /etc/resolv.conf /etc/resolv.conf.original
sudo ln -s /run/systemd/resolve/stub-resolv.conf /etc/resolv.conf
sudo systemctl restart systemd-resolved.service

This worked for me!