@TartanSpartan Last night I was too sleepy to read English writtings. Now I 'm fully awake. 
I didn't know .ovpn file can be specified as mncli command's argument or doing so mncli can create VPN setting file which is available for network-manager-openvpn-gnome or VPN tool.
I always use 'ip' command for network settings or getting information of network but now I know 'nmcli' is very useful, too.
Thank you for letting me know it. I'll learn much more about NetworkManager. 
@TartanSpartan Congratulations!
Anyway I'm very happy to know you can achieve a VPN connection. 
@TartanSpartan Hello
I'm sorry.
Your VPN provider doesn't use tsl-auth certification.
So my settings wouldn't be help for you.
If connection results in failure on UT I still recommend you to compare setting files but you can test the ovpn out via the command line as Fuseteam said. Because it shows the reason of failure immediately.
sudo openvpn [ovpnfile name]
Password for sudo command is required first then usename & password for VPN are required.
(Note that password phrase may not be shown even if you input)
If it works massages end with like following.
Sun Jul 26 09:05:55 2020 Initialization Sequence Completed
Thank you.
@TartanSpartan Oh no, now I found Premiumize VPN's OVPN file includes CA certification but no tls-auth certification. I missed that.
So maybe you made settings by following this tutorial.
https://www.premiumize.me/plugins?os=ubuntu&tool=openvpn
Making VPN settings with Network Manager Gnome on Ubuntu Desktop, setting file is created in '/etc/NetworkManager/system-connections' directory as well as with VPN Tool on UT.
If connection succeed on Ubuntu Desktop and fail on UT you'd better compare both files. Something might be different from each other.
Would you show me what is different between two setting files?
@TartanSpartan Here's my settings
Certification files are just text files.
I used files which created by Network Manager Gnome and files which I myself copied and pasted from OVPN file and both worked fine.
If you give settings to VPN like above and it does't work ask me again.
I hope it works fine.
@TartanSpartan I would help you anyway.
But as you know I'm not a native speaker of English so I'm sorry for my bad or wrong expressions.
I have many things I want let you know but it's hard for me to write. So I will upload the pictures of my settings. Wait a minute, please.
@BigB I don't know I could help you or not but I want to know this
.
Can Desktop Linux with the generated .pem files connect successfully to PiVPN server from outside of LAN?
@ToxyPoxy I'm very sorry that I've been hi-jacked your subject for a long time.
At last vpn connection works!
I use client/tls certification files which is created by Network-Manager-Gnome client on Ubuntu Desktop.
Network-Manager-Gnome client automatically crates these files in '~/.cert/nm-openvpn' directory when you import ovpn file downloaded from Nordvpn's web site.
When I looked into the contents of ovpn file it said like this.
comp-lzo no
So when I configured VPN tool on UT I didn't put a check on 'USE LZO data compression'.
But last night I found this warning from '/var/log/syslog'.
ubuntu-phablet nm-openvpn[13678]: WARNING: 'comp-lzo' is present in remote config but missing in local config, remote='comp-lzo'
Putting a check on 'USE LZO data compression' solve the problem. NordVPN's home page tells me the connection is safe.
Network-Manager-Gnome client automatically sets all items in setting form as written in ovpn file, I set VPN tool on UT as Network-Manager-Gnome client did.
I think this is the easiest way to setup NordVPN connection. This works for ProtonVPN's setting as well.
I hope this helps you.
Thank you.
Considering something is wrong with my Nexus5's system and tryng it again from the beggining I flashed my Nexus5. All things I did before I tried to connect VPN are only to make sshd enable. To get straight to the point, I got the same result. VPN connection is established but name resolutuion doesn't work.
I compared state of networks between Ubuntu Desktop 18.04 LTS and Ubuntu Touch OTA-12.
Note that both of them are on the same local network xx.yy.204.0/24.
First, Ubuntu Desktop 18.04 TLS.
Vpn configuration is set by Network-Manager-Gnome(GUI).
It's very easy to configure and works perfectly.
( VPN OFF )
$ ip route show
default via xx.yy.204.254 dev wlp3s0 proto dhcp metric 600
169.254.0.0/16 dev wlp3s0 scope link metric 1000
xx.yy.204.0/24 dev wlp3s0 proto kernel scope link src xx.yy.204.107 metric 600
( VPN ON )
$ ip route show
default via 10.8.2.1 dev tun0 proto static metric 50
default via xx.yy.204.254 dev wlp3s0 proto dhcp metric 600
10.8.2.0/24 dev tun0 proto kernel scope link src 10.8.2.8 metric 50
169.254.0.0/16 dev wlp3s0 scope link metric 1000
xx.yy.204.0/24 dev wlp3s0 proto kernel scope link src xx.yy.204.107 metric 600
xx.yy.204.254 dev wlp3s0 proto static scope link metric 600
212.102.51.212 via xx.yy.204.254 dev wlp3s0 proto static metric 600
$ ping -c1 10.8.2.8
PING 10.8.2.8 (10.8.2.8) 56(84) bytes of data.
64 bytes from 10.8.2.8: icmp_seq=1 ttl=64 time=0.073 ms
--- 10.8.2.8 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.073/0.073/0.073/0.000 ms
$ ping -c1 10.8.2.1
PING 10.8.2.1 (10.8.2.1) 56(84) bytes of data.
64 bytes from 10.8.2.1: icmp_seq=1 ttl=64 time=11.7 ms
--- 10.8.2.1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 11.706/11.706/11.706/0.000 ms
$ ping -c1 212.102.51.212
PING 212.102.51.212 (212.102.51.212) 56(84) bytes of data.
64 bytes from 212.102.51.212: icmp_seq=1 ttl=58 time=9.18 ms
--- 212.102.51.212 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 9.186/9.186/9.186/0.000 ms
Second, Ubuntu Touch OTA-12.
Vpn configuration is set by VPN Tool(GUI).
Client and TLS Certification files are ported from Ubuntu Desktop I mension above.
( VPN OFF )
§ ip route show
default via xx.yy.204.254 dev wlan0 proto static metric 600
xx.yy.204.0/24 dev wlan0 proto kernel scope link src xx.yy.204.249 metric 600
( VPN ON )
§ ip route show
default via 10.8.0.1 dev tun0 proto static metric 50
default via xx.yy.204.254 dev wlan0 proto static metric 600
10.8.0.0/24 dev tun0 proto kernel scope link src 10.8.0.4 metric 50
xx.yy.204.0/24 dev wlan0 proto kernel scope link src xx.yy.204.249 metric 600
212.102.51.212 via xx.yy.204.254 dev wlan0 proto static metric 600
§ ping -c1 10.8.0.4
PING 10.8.0.4 (10.8.0.4) 56(84) bytes of data.
64 bytes from 10.8.0.4: icmp_seq=1 ttl=64 time=0.117 ms
--- 10.8.0.4 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.117/0.117/0.117/0.000 ms
§ ping -c1 10.8.0.1
PING 10.8.0.1 (10.8.0.1) 56(84) bytes of data.
--- 10.8.0.1 ping statistics ---
1 packets transmitted, 0 received, 100% packet loss, time 0ms
§ ping -c1 212.102.51.212
PING 212.102.51.212 (212.102.51.212) 56(84) bytes of data.
64 bytes from 212.102.51.212: icmp_seq=1 ttl=58 time=11.2 ms
--- 212.102.51.212 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 11.278/11.278/11.278/0.000 ms
I don't know what makes the difference betweem them.
Do I make big mistake?
What do I have to do next?
@uzanto I'm sorry I can't explain what is happening well.
While VPN is ON the result of 'ip route' shows that tun0 interface is created and up. And the button's color of VPN Tool turns into green.
Doesn't this mean VPN connection is established successfully?
@Seba I gave a try to connect but the result was the same.
VPN connection seems to be activated like a picture I uploaded before
but my nexus5 can't go anywhere.
Web Browser shows
'Error: net::ERR_NAME_RESOLUTION_FAILED’
This is exactly the same result as I got before.
Thank you Seba.
You must be right.
I'm sure something else is wrong with my Nexus5.
I have no idea why my Nexus5 get to be disable to resolve name when
VPN is on. When VPN is off it can access to NordVPN page without
any problem.
@Seba I couldn't have found this link.
This is what I've looking for.
Anyway I'll try this later.
Thank you so much.
@uzanto I'm trying with udp.
Connection itself seems to be OK.
So problem of name resolving may be caused by other reason.
But I wonder UT's VPN setting has no DNS settings
like Network Manager of Ubuntu Desktop.
I wonder how is DNS information given to Phone
and there is no /etc/resolv.conf on UT,
Thank you.
I downloaded ovpn files from the link.
Dividing ovpn file into CA certificate and TLS key file
and Using VPN editor I could established VPN connection.
But somehow after establishing connection name resolving
doesn't work and my Nexus5 can't go anywhere.
I did the same about ProtonVPN and the result is the same.
On my Ubuntu Desktop, Using Network Manager all works fine
both ProtonVPN and NordVPN.
I hope this may help you.
Double-Tap Wake/Sleep feature on Android is very useful.
I wish I could use the feature on UT.
