实验6：开源控制器实践——RYU

一、实验目的

1. 能够独立部署RYU控制器；
2. 能够理解RYU控制器实现软件定义的集线器原理；
3. 能够理解RYU控制器实现软件定义的交换机原理。

二、实验环境

Ubuntu 20.04 Desktop amd64

三、实验要求

（一）基本要求

1. 搭建下图所示SDN拓扑，协议使用Open Flow 1.0，并连接Ryu控制器，通过Ryu的图形界面查看网络拓扑。
    

    

    

2. 阅读Ryu文档的The First Application一节，运行当中的L2Switch，h1 ping h2或h3，在目标主机使用 tcpdump 验证L2Switch，分析L2Switch和POX的Hub模块有何不同　　　　创建L2Switch.py文件,并保存在目录/home/用户名/学号/lab6/中

 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
 from ryu.ofproto import ofproto_v1_0

 class L2Switch(app_manager.RyuApp):
     OFP_VERSIONS = [ofproto_v1_0.OFP_VERSION]

     def __init__(self, *args, **kwargs):
         super(L2Switch, 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)]

         data = None
         if msg.buffer_id == ofp.OFP_NO_BUFFER:
              data = msg.data

         out = ofp_parser.OFPPacketOut(
             datapath=dp, buffer_id=msg.buffer_id, in_port=msg.in_port,
             actions=actions, data = data)
         dp.send_msg(out)

 RYU的L2Switch模块和POX的Hub模块都采用洪泛转发，但不同之处在于：可以在pox的Hub模块运行时查看流表，而无法在ryu的L2Switch模块运行时查看到流表

1. 编程修改L2Switch.py，另存为L2xxxxxxxxx.py，使之和POX的Hub模块的变得一致？（xxxxxxxxx为学号）

from ryu.base import app_manager
from ryu.ofproto import ofproto_v1_3
from ryu.controller import ofp_event
from ryu.controller.handler import MAIN_DISPATCHER, CONFIG_DISPATCHER
from ryu.controller.handler import set_ev_cls
 
 
class hub(app_manager.RyuApp):
    OFP_VERSIONS = [ofproto_v1_3.OFP_VERSION]
 
    def __init__(self, *args, **kwargs):
        super(hub, self).__init__(*args, **kwargs)
 
    @set_ev_cls(ofp_event.EventOFPSwitchFeatures, CONFIG_DISPATCHER)
    def switch_feathers_handler(self, ev):
        datapath = ev.msg.datapath
        ofproto = datapath.ofproto
        ofp_parser = datapath.ofproto_parser
 
        # install flow table-miss flow entry
        match = ofp_parser.OFPMatch()
        actions = [ofp_parser.OFPActionOutput(ofproto.OFPP_CONTROLLER, ofproto.OFPCML_NO_BUFFER)]
        # 1\OUTPUT PORT, 2\BUFF IN SWITCH?
        self.add_flow(datapath, 0, match, actions)
 
    def add_flow(self, datapath, priority, match, actions):
        # 1\ datapath for the switch, 2\priority for flow entry, 3\match field, 4\action for packet
        ofproto = datapath.ofproto
        ofp_parser = datapath.ofproto_parser
        # install flow
        inst = [ofp_parser.OFPInstructionActions(ofproto.OFPIT_APPLY_ACTIONS, actions)]
        mod = ofp_parser.OFPFlowMod(datapath=datapath, priority=priority, match=match, instructions=inst)
        datapath.send_msg(mod)
 
    @set_ev_cls(ofp_event.EventOFPPacketIn, MAIN_DISPATCHER)
    def packet_in_handler(self, ev):
        msg = ev.msg
        datapath = msg.datapath
        ofproto = datapath.ofproto
        ofp_parser = datapath.ofproto_parser
        in_port = msg.match['in_port']  # get in port of the packet
 
        # add a flow entry for the packet
        match = ofp_parser.OFPMatch()
        actions = [ofp_parser.OFPActionOutput(ofproto.OFPP_FLOOD)]
        self.add_flow(datapath, 1, match, actions)
 
        # to output the current packet. for install rules only output later packets
        out = ofp_parser.OFPPacketOut(datapath=datapath, buffer_id=msg.buffer_id, in_port=in_port, actions=actions)
        # buffer id: locate the buffered packet
        datapath.send_msg(out)

 四、个人总结

        本次实验难度适中，先验证ryu基本功能，再了解背后实现流程。先启用ryu控制器，而后打开Ryu验证L2Switch，最后再进行拓扑构建，即可使用tcpdump顺利验证实验结论。RYU的L2Switch模块和POX的Hub模块都采用洪泛转发，但不同之处在于：可以在pox的Hub模块运行时查看流表，而无法在ryu的L2Switch模块运行时查看到流表。