Source : http://blog.wensheng.org/2015/05/fixing … buntu.html
fixing VPN problem in Ubuntu
I set up VPN in Ubuntu 14.04, but when I tried to turn it on in NetworkManager, I kept getting errors like “No suitable device found”, “Could not find source connection” in /var/log/syslog.
The problem turned out to be that my ethernet connection was not managed by NetworkManager. “nmcli c” didn’t show my wired connection.
The solution:
Edit /etc/NetworkManager/NetworkManager.conf, in section [ifupdown], change “managed=false” to “managed=true”, then do a:
“sudo service network-manager restart”
Now both vpn and ethernet connections are managed by NetworkManager, turning on VPN just works.
p.s.
About Having DNS Issues when connected to a VPN
source : https://askubuntu.com/questions/320921/having-dns-issues-when-connected-to-a-vpn-in-ubuntu-13-04
Question
I am connecting to a Cisco VPN Server using vpnc. Once connected, my machine was unable to automatically update DNS setting from the new VPN. I tested by temporarily changing /etc/resolv.conf with the proper nameserver and search domain, and everything worked. This is obviously not a long term solution, so I added an additional DNS server and search domain to the VPN settings in Network manager. With those settings in place, resolvconf does add the search domain, but not the DNS IP, and I still cannot do any lookups.
What is my next step in configuring or troubleshooting from here?
Answer
First make sure that there are no lines beginning with nameserver in any files in /etc/resolvconf/resolv.conf.d. If /etc/resolvconf/resolv.conf.d/tail is a symbolic link to target original, make it point to /dev/null.
Second, disconnect from the VPN. Edit /etc/NetworkManager/NetworkManager.conf
$ sudo gedit /etc/NetworkManager/NetworkManager.conf
and comment out
dns=dnsmasq
(i.e., add a # so that it looks like the following)
#dns=dnsmasq
and then
sudo service network-manager restart