Recently, I upgraded to 18.04 from 16.04 on Lenovo Thinkpad P50. When I come home, and wake up laptop from sleep, it connects to wifi connection but internet connectivity is not established. I can ping to router but cannot ping to any website. I restarted network-manager service but it does not wor.
After upgrading, by default network manager was not managing eth0 and wlan0 interfaces defined in
To enable network manager to manage these interfaces, open
sudo gedit /etc/NetworkManager/NetworkManager.conf
It solved the problem.