dnsmasq sometimes resolves things, sometimes it doesn't
I have this inside my internal network, and I solved it by disabling the local forwarding nameserver controlled by NetworkManager (dnsmasq).
To do that, you need to edit /etc/NetworkManager/NetworkManager.conf and comment out the “dns=dnsmasq” line in the "[main]" section.
Open a terminal, and run
sudo nano /etc/NetworkManager/NetworkManager.conf
Then make sure that the line
dns=dnsmasq
is commented out like this:
#dns=dnsmasq
Now, restart network-manager with the following command, and everything should work properly.
sudo restart network-manager