Sending and processing a hello message
The OFPT_HELLO
message is used by both the switch and the controller to identify and negotiate the OpenFlow version supported by both the devices. Hello messages should be sent from the switch once the TCP/TLS connection is established and are considered part of the communication channel establishment procedure.
To send a hello message, the switch should have established the TCP/TLS connection defined in the Connection setup on TCP and TLS recipe in Chapter 1, OpenFlow Channel Connection Establishment (Part 1).
As hello messages are transmitted by both the switch and the controller, the switch should be able to send, receive, and process the hello message. The following section explains these procedures in detail.