Neutron provides Networking-as-a-service in the OpenStack ecosystem. Networking functionalities are provided by plugins that implement well-defined Neutron APIs. Among many, the Open vSwitch plugin (OVS) is possibly the most widely used. Any practical OpenStack installation has complicated networking configuration and verifying it manually is time consuming and error prone. DON, written primarily in Python, and available as a dashboard in OpenStack Horizon, Libery release, is a network analysis and diagnostic system and provides a completely automated service for verifying and diagnosing the networking functionality provided by OVS. This service verifies (or points out deviations) that the user configuration is indeed reflected in the underlying infrastructure and presents the results in an intuitive graphical display.