Upgraded to Debian 9.12, now have no network connection

Solution 1:

It seems that during the upgrade process your network device got renamed. Change every occurrence of enp0s3 to ens3 in /etc/network/interfaces, and it should get the IP address from the DHCP server.

Solution 2:

This is caused by the configuration option net.ifnames=1 which is enabled by default in Debian 9.

You can either:

• Update the interface name(s) in /etc/network/interfaces
• Set the net.ifnames=0 as a kernel parameter

See https://wiki.debian.org/NetworkInterfaceNames for more details