在RYU中实现交换机的功能

from ryu.base import app_manager

from ryu.controller import ofp_event

from ryu.controller.handler import CONFIG_DISPATCHER, MAIN_DISPATCHER

from ryu.controller.handler import set_ev_cls

from ryu.ofproto import ofproto_v1_3

from ryu.lib.packet import packet

from ryu.lib.packet import ethernet

 

 

class SimpleSwitch13(app_manager.RyuApp):

    OFP_VERSIONS = [ofproto_v1_3.OFP_VERSION]//OpenFlow1.3版本

 

    def __init__(self, *args, **kwargs):

        super(SimpleSwitch13, self).__init__(*args, **kwargs)

        self.mac_to_port = {}\\MAC位址表，用于存放MAC地址和端口之间的映射

\\@set_ev_cls表示事件修饰符，任何一个OpenFlow讯息都会产生一个对应的事件，事件类别的名称规则为

\\ryu.controller.ofp_event.EventOFP+<OpenFlow讯息名称>

\\第二个参数表示交换机的状态。表示在CONFIG_DISPATCHER的交换机状态下，接收到交换机的\\SwitchFeatures讯息就会执行对应事件处理**_handle（）函数。

    @set_ev_cls(ofp_event.EventOFPSwitchFeatures, CONFIG_DISPATCHER)

    def switch_features_handler(self, ev):

\\datapath是交换机实体

        datapath = ev.msg.datapath

        ofproto = datapath.ofproto

        parser = datapath.ofproto_parser

 

        # install table-miss flow entry

        #

        # We specify NO BUFFER to max_len of the output action due to

        # OVS bug. At this moment, if we specify a lesser number, e.g.,

        # 128, OVS will send Packet-In with invalid buffer_id and

        # truncated packet data. In that case, we cannot output packets

        # correctly.

\\为交换机的流表新增Table-miss Flow Entry项，用于封包在无法匹配到流表项后与之匹配。

\\match表示匹配约束，为空则说明可以匹配所有封包。action表示匹配成功后执行的操作，此处 

\\为向Controller端口发送最大数据长度的封包。OFPCML_NO_BUFFER表示不需要在交换机上缓存封包

\\将封包整体发给controller。优先级为0，即最低的优先权。

        match = parser.OFPMatch()

        actions = [parser.OFPActionOutput(ofproto.OFPP_CONTROLLER,

                                          ofproto.OFPCML_NO_BUFFER)]

        self.add_flow(datapath, 0, match, actions)

 

    def add_flow(self, datapath, priority, match, actions):

        ofproto = datapath.ofproto

        parser = datapath.ofproto_parser

\\Entry的Instruction项，指定为output action中的动作，OFPIT_APPLY_ACTIONS表示动作立即执行

        inst = [parser.OFPInstructionActions(ofproto.OFPIT_APPLY_ACTIONS,

                                             actions)]

\\FlowMod讯息的类别为OFPFlowMod，使用FlowMod所产生的实体透过datapath.send_msg()来发送、、\\FlowMod讯息给OpenFlow交换机。

        mod = parser.OFPFlowMod(datapath=datapath, priority=priority,

                                match=match, instructions=inst)

        datapath.send_msg(mod)

\\交换机的一般状态下接收交换机的packet-In讯息所作处理

    @set_ev_cls(ofp_event.EventOFPPacketIn, MAIN_DISPATCHER)

    def _packet_in_handler(self, ev):

        msg = ev.msg

        datapath = msg.datapath

        ofproto = datapath.ofproto

        parser = datapath.ofproto_parser

        in_port = msg.match[‘in_port‘]\\表示封包进入交换器待转发的端口号

 

        pkt = packet.Packet(msg.data)

        eth = pkt.get_protocols(ethernet.ethernet)[0]

\\获取目的和源Mac地址

        dst = eth.dst

        src = eth.src

\\获取OpenFlow交换器的标识ID

        dpid = datapath.id

        self.mac_to_port.setdefault(dpid, {})

 

        self.logger.info("packet in %s %s %s %s", dpid, src, dst, in_port)

\\每个datapath建立一个mac位址表，将host的mac地址与交换机对应的端口号进行映射。

        # learn a mac address to avoid FLOOD next time.

        self.mac_to_port[dpid][src] = in_port

\\判断目的Mac地址是否存在于Mac位址表中，若不存在则进行洪泛

        if dst in self.mac_to_port[dpid]:

            out_port = self.mac_to_port[dpid][dst]

        else:

            out_port = ofproto.OFPP_FLOOD

 

        actions = [parser.OFPActionOutput(out_port)]

 

        # install a flow to avoid packet_in next time

\\添加交换机中的流表项

        if out_port != ofproto.OFPP_FLOOD:

            match = parser.OFPMatch(in_port=in_port, eth_dst=dst)

            self.add_flow(datapath, 1, match, actions)

 

        data = None

        if msg.buffer_id == ofproto.OFP_NO_BUFFER:

            data = msg.data

\\将Packet-Out讯息对应的类别OFPPacketOut的实体发送给交换机

        out = parser.OFPPacketOut(datapath=datapath, buffer_id=msg.buffer_id,

                                  in_port=in_port, actions=actions, data=data)

        datapath.send_msg(out)