Packet Processor (Python version)

A Simple External Packet Processor Using Python

DNOS provides a gRPC based event notification service that can be used in management applications to receive incoming events such as PACKET_IN events. In this tutorial we explain how you can use that service in a python application to receive incoming packets from ONOS.

1. Follow the installation instructions here to prepare your setup ready.

2. Clone the repository of the sample python applications as follows:

   git clone https://github.com/dnosproject/dnos-apps-python.git
   

3. Run a mininet emulation scenario as follows:

   $ sudo mn --topo=linear,2 --controller=remote,ip=127.0.0.1
   

4. Run the samplepacketprocessor app under dnos-apps-python directory as follows.

   bazel run samplepacketprocessor:samplepacketprocessor 
   

5. Run pingall from mininet command line. After running the pingall, the first incoming ICMP packets will be sent to the controller and the event notification service in DNOS application send them to the external sample packet processer application. The application prints an output like this:

   An IPv4 packet has been received
   An IPv4 packet has been received
   An IPv4 packet has been received
   An IPv4 packet has been received
   

How does the sample packet processor application work?

1. First of all, we need to create a gRPC channel and register the client in the remote gRPC server which is running in DNOS application as follows:

     channel = grpc.insecure_channel('localhost:50051')
     eventNotificationStub = ServicesProto_pb2_grpc.EventNotificationStub(channel)
   
     request = EventNotificationProto_pb2.RegistrationRequest(clientId = "packet_processor_python")
     topic = EventNotificationProto_pb2.Topic(clientId = "packet_processor_python"
                                              , type = 0)
   
     # Register to PACKET_EVENT
     response = eventNotificationStub.register(request)
   

2. Second, we need subcribe to PACKET_EVENT to receive incoming packets from DNOS. Then we will need to go through the list of incoming events (in this example packet events) and process incoming packets using a third-party library to extract its information. In this example, we want to print a message whenever we receive an IPv4 packet.

   eventObserver = eventNotificationStub.onEvent(topic)
   for event in eventObserver:
          pktContext = event.packetContext
          if pktContext is None:
              return
          inboundPkt = pktContext.inboundPacket
          pkt = packet.Packet(inboundPkt.data)
          for p in pkt:
              if type(p)!= str:
                 if p.protocol_name == "ipv4":
                     print("An IPv4 packet has been received")
   

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