DHClient Not Acquiring New Lease After Disconnecting and Reconnecting Ethernet cable

[Hagen Kuehn]

isc-dhclient-4.3.3 does not acquire a new DHCP lease when the Ethernet cable was disconnected and reconnected.

This problem is observed with Ubuntu 16.04 whereas it's working with Ubuntu 14.04 (i.e. isc-dhclient-4.2.4).

The Problem:
When using Virtualbox 5.0.20 and Vagrant 1.8.1, SSH connection fails after the Ubuntu 16.04 VM was suspended and then started again from the saved state.

As of this Virtualbox bug https://www.virtualbox.org/ticket/15412 it appears from Virtualbox 5.0.20 onwards, Virtualbox disconnects the Ethernet cable for 5 seconds in order to trigger a DHCP lease request. Since this is not the case with isc-dhclient-4.3.3 on Ubuntu 16.04 any more, Virtualbox is waiting for network traffic endlessly in order to infer the IP address of the VM, which is in turn required for Virtualbox NAT Forwarding to work.

External associated bugs:
https://www.virtualbox.org/ticket/15412
https://github.com/mitchellh/vagrant/issues/7306