Ubuntu 17 uses resolved for DNS resolution. This does not always work very well with OpenVPN. When your DNS is not resolved correctly (always externally instead of internal addresses), try to use this fix here.
Update the line in /etc/nsswitch.conf:
`hosts: files mdns4_minimal [NOTFOUND=return] resolve [!UNAVAIL=return] dns myhostname`
into
`hosts: files mdns4_minimal [NOTFOUND=return] dns resolve [!UNAVAIL=return] myhostname`
This changes the order in which the calls are resolved.
Brain/Drain/Pain 
Well, thank you it really helped me. I was about to give up using a VPN on my machine.
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