The OpenFlow switch should maintain the connectivity to all controllers.If for any reason the switch loses the connection to all configured controllers, then the switch should follow the procedure defined in this section.
If a switch loses its connection with all the connected or configured controllers, then the switch should immediately enter either fail secure mode or fail standalone mode depending upon the switch configuration or implementation. The connection loss can be identified by either OpenFlow echo request timeouts or TLS session timeouts or other disconnection procedures such as TCP socket close, etc.
When the switch is in fail secure mode, the switch should drop all the packets and messages destined to controllers. However, all the flow entries programmed by the controller should persist in the switch and expire based on the configured timeout value in fail secure mode.
The fail standalone mode is usually possible only on Hybrid switches. When a switch is in fail standalone mode, the switch should act as a legacy Ethernet switch or router and should process all the packets.
Upon connecting to a controller again, the existing flow entries remain intact. The controller can delete all the existing flow entries, if desired. The switch can be configured to start up with the operational mode either as fail secure mode or fail standalone mode until it successfully connects to a controller.