OpenFlow in Ryu

OpenFlow in Ryu

The communication processing and a handling of the foundational OpenFlow protocol, e.g. hello, echo, is implemented in Ryu framework. A user Ryu application can implement a handling of necessary OpenFlow event.

An event handler is called with an event object as an argument. The event object is representation of the OpenFlow message which Ryu received from OpenFlow switch. The object is a subclass of ryu.controller.ofp_event.EventOFPMsgBase class.

class EventOFPMsgBase(event.EventBase):
    def __init__(self, msg):
        super(EventOFPMsgBase, self).__init__()
        self.msg = msg

Each event class is created dynamically from the corresponding OpenFlow message class. Because of that, you cannot find the code of an event class explicitly.

The name of event class is 'Event' + corresponding message class name. For example, the event class for OFPPacketIn message is EventOFPPacketIn.

The msg attribute of the event class holds the message class instance which created it.

Each OpenFlow message class is a subclass of ryu.ofproto.ofproto_parser.MsgBase class. The MsgBase class is defined as follows, so every OpenFlow message class have those attributes.

class MsgBase(object):
    def __init__(self, datapath):
        self.datapath = datapath
        self.version = None
        self.msg_type = None
        self.msg_len = None
        self.xid = None
        self.buf = None

Attribute	Description
datapath	A ryu.controller.controller.Datapath instance associated with the OpenFlow switch
version	OpenFlow protocol version
msg_type	Type of OpenFlow message
msg_len	Length of the message
xid	Transaction id
buf	Raw data

The following example is handling EventOFPPacketIn and sending OFPPacketOut.

from ryu.base import app_manager
from ryu.controller import ofp_event
from ryu.controller.handler import MAIN_DISPATCHER
from ryu.controller.handler import set_ev_cls


class MySwitch(app_manager.RyuApp):
    def __init__(self, *args, **kwargs):
        super(MySwitch, self).__init__(*args, **kwargs)

    @set_ev_cls(ofp_event.EventOFPPacketIn, MAIN_DISPATCHER)
    def packet_in_handler(self, ev):
        msg = ev.msg
        dp = msg.datapath
        ofp = dp.ofproto
        ofp_parser = dp.ofproto_parser

        actions = [ofp_parser.OFPActionOutput(ofp.OFPP_FLOOD)]
        out = ofp_parser.OFPPacketOut(
            datapath=dp, buffer_id=msg.buffer_id, in_port=msg.in_port,
            actions=actions)
        dp.send_msg(out)

The following page describes the detail of OpenFlow messages.

OpenFlow V1.0 messages
OpenFlow V1.2 messages
OpenFlow V1.3 messages