These messages are used to directly manage or inspect the state of the switch:
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Handshake: Upon the establishment of the TLS session (for example, the TLS TCP session on port 6633), the controller sends an OFPT_FEATURES_REQUEST message to the switch and the OpenFlow switch reports back (via the OFPT_FEATURES_REPLY message) the features and capabilities that it has and that it supports. The datapath_id field uniquely identifies an OpenFlow switch (datapath). It is a 64-bit entity and the lower 48 bits are intended for the switch MAC address, while the top 16 bits are up to the manufacturer. Datapath identifier (datapath_id) has a maximum number of packets the switch can buffer when sending packets to the controller ...
