Role-Request

In a network provided with multiple controllers for redundancy purpose, the roles of each controller are distinct and are assumed per time. The various roles that can be assumed by an OpenFlow controller include the following:

• Master role: In this role, the controller has complete access to all the switches. It executes commands such as packet-out flow-mod, table-mod, port-mod, which are capable of modifying the state of the switch by receiving asynchronous messages from the switch. Every other controller connected to the switch assumes the Slave role automatically.
• Slave role: Slave role is assumed by the controller when one of the peer controllers connected to the switch assumes the role of a master; commands capable of modifying the switch are not run by this controller. In the event that the switch receives such commands from a slave controller, it replies with an OFPT_ERROR message.
• Equal role: This is the default role assumed by all controllers connected to a switch, and it allows each controller to send asynchronous messages and commands to the switch.