Problem scenario
You are connecting to a VM in Oracle VirtualBox from a desktop. The pings to the VM are not responding. What should you do?
Solution
Go to Devices -> Network -> Network Settings
The "Attached to:" setting hould be "Bridged Adapter"
The "Name" setting should what you think is appropriate. Not uncommonly this will be en0 Wi-Fi.
Expand the "Advanced" settings. Promiscuous mode should be "Allow All." The "Cable connected" option should be checked.