System and method for controller-initiated simultaneous discovery of the control tree and data network topology in a software defined network

A method as implemented in a transit switch in a software defined network (SDN), the SDN further comprising a controller storing an in-band control tree, the control tree spanning switches as an overlay to the SDN with the controller as the root of the control tree, the controller connected to at least the transit switch in the control tree, and the transit switch having at least one, first-degree, neighbor transit switch also in the control tree and having at least another, first-degree, neighbor switch that is not in the control tree, the method comprising:

• a. receiving, from the controller, a packet-out message with an LLDP packet as its payload;
• b. extracting the LLDP packet from the payload of the packet-out message;
• c. multicasting the LLDP packet through all active ports of the transit switch to the neighbor transit switch and neighbor switch, wherein the neighbor transit switch in the control tree generates and transmits, to the controller, a first packet-in message using the received LLDP packet as the payload;
• d. receiving a second packet-in message from a neighbor switch not in the control tree, with the neighbor switch generating and transmitting the packet-in message with a hello message as its payload, where the packet-in message is sent over the same port in the neighbor switch that received the LLDP packet transmitted in (c);
• and
• e. forwarding the packet-in message to the controller,
• wherein the container adds a new link to the control tree for the neighbor switch that sent the second packet-in message.

A controller in a software defined network (SDN), the controller storing an in-band control tree, the control tree spanning switches as an overlay to the SDN with the controller as the root of the control tree, the controller connected to at least a transit switch in the control tree, and the transit switch having at least one, first-degree, neighbor transit switch also in the control tree and having at least another, first-degree, neighbor switch that is not in the control tree, the controller comprising:

• a. a control discovery subsystem, which initiates and manages control network discovery, and:
• (1) generates and transmits, to the transit switch, a packet-out message with an LLDP packet as its payload, wherein the transit switch:
• receives the packet-out message, extracts the LLDP packet from its payload, and multicasts the LLDP packet through all its active ports to the neighbor transit switch and neighbor switch, (2) receives, from the neighbor transit switch in the control tree, a first packet-in message, with the first packet-in message being generated by the neighbor transit switch using the received LLDP packet as the payload, and (3) receives, from the neighbor switch not in the control tree, a second packet-in message with a hello message as its payload, with the second packet-in message being sent over the same port in the neighbor switch that received the LLDP packet transmitted in (1) and via the transit switch connected to the controller which then forwards the second packet-in message to the controller;
• b. a topology discovery subsystem that derives the existence of connections between switches based on received first and second packet-in messages by the control discovery subsystem;
• and
• c. a topology database storing data network and control tree topologies.