Questions[dns](ubuntu)

I just installed a new Ubuntu Server 18.04. I set my hostname hostnamectl set-hostname ****.openbayou.biz and I set /etc/hosts:

127.0.0.1 localhost
[ip address] ****.openbayou.biz hostname
# The following lines are desirable for IPv6 capable hosts
[ip6 address] *****.openbayou.biz hostname
::1     localhost ip6-localhost ip6-loopback
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

I also installed OSSEC to monitor for new files, errors and changes to my server and I'm now getting these alerts:

Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018- 
0001, retrying transaction with reduced feature level UDP.`

It's now repeating itself:

systemd-resolved[3195]: message repeated 4 times: [ Server returned error 
NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction 
with reduced feature level UDP.]

I've looked online for a solution and nobody is reporting this issue.

When I connect to a VPN network through Gnome Network-manager I lose DNS resolution and in practice, I cannot access resources inside the VPN network or outside.

When I was using Ubuntu 16.04 and I was using the VPN, the "/etc/resolv.conf/" file would contain the DNS servers of the (VPN) network I had connected. Now it always contains the following entries:

nameserver 127.0.0.53
search myprovider.com

From what I have understood 127.0.0.53 is the address of the DNS stub used by the system-resolved.

I suspect that this is a bug because the VPN was working fine the Ubuntu 16.04. Is there any way that I can set the DNS servers of my network when I am using a VPN service?

Update:

I tried connecting to the OpenVPN network with the configuration file attached at the end of the post, but I get the following error:

 Authenticate/Decrypt packet error: cipher final failed

I have verified that the server uses lzo compression and I have enabled it as well. The connection stays active but I cannot navigate to any page inside or outside the VPN.

In the configuration file listed below, I have included the solutions posted in the replies

 client
 dev tun
 proto udp
 remote openvpn.bibsys.no 1194
 remote my-server-2 1194
 resolv-retry infinite
 nobind
 user myuser
 group myuser
 persist-key
 persist-tun
 ca ca-cert.pem
 cert openvpn.crt
 key openvpn.key
 cipher AES-256-CBC
 comp-lzo yes
 script-security 2
 up /etc/openvpn/scripts/update-systemd-resolved
 down /etc/openvpn/scripts/update-systemd-resolved
 down-pre

How can I disable systemd-resolved in Ubuntu 17.04?

Disabling it with systemctl disable didn't work, the service seems to be restarted (by Networkmanager?)

How can I flush the DNS on Ubuntu 17.04?

I seem to have a few DNS issues at the moment since upgrading to 17.04 from 16.10 and went to flush the DNS but I can't find how to.

Can anyone tell me please?

I just updated the DNS record (ns1, ns2, ns3.myhostingcompany.com) for a site I've got hosted, but I still get the domain registrar parking page.

I'd like to see if the problem is Ubuntu's cached DNS records. Is there a way to clear Ubuntu's DNS cache? (if such a thing exists?)