When a flow is first programmed into a switch connected to the controller, the controller sends a flow mod message to the switch, and the flow is also remembered in the md-sal config data store. The flow remains in the data store until it is deleted by an application.

Now, when a switch restarts, the controller currently does not replay flows that are present in the md-sal config data store to the switches where they were originally programmed. In other words, after a switch reconnects to the controller, the controller does not perform a state reconciliation, where the controller would read the state of the switch, delete flows present in the switch but not present in controller's config data store and program flows that are not present in the switch but present in the controller's data store.

Such state reconciliation must be performed by the controller.