Ryu controller - deal with openflow packets notes

- Controller receives a  packet from a switch if the switch failed to look up it's flow table
- Get incoming packet message, src mac/ip, dst mac/ip, ofproto, ... whatever you want
- Learn a switch-port-mac_address entry
- See what you want to do

• design an action: OFPActionOutput, OFPActionSetQueue, OFPActionSetField, ...
• design an match: OFPMatch
• add a flow: 
• OFPInstructionActions create instruction (input: action)
• OFPFlowMod create flow modification request
• datapath.send_msg to send request
• ask switch to forward this pkt
• OFPPacketOut to create send packet request 
• datapath.send_msg to send request

- All classes are in ryu/ofproto/ofproto_[version]_parser.py. See more attributes or methods in this python module.