实验6：开源控制器实践——RYU

（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。

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)

h1pingh2

h1pingh3

分析L2Switch和POX的Hub模块有何不同
Hub和L2Switch模块都是洪泛转发，但L2Switch模块下发的流表无法查看，而Hub模块下发的流表可以查看

3.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)

（二）个人总结
一开始在通过Ryu的图形界面查看网络拓扑时出现了问题，当我运行ryu-manager ryu/ryu/app/gui_topology/gui_topology.py --observe-links的时候，系统报错找不到目标文件，尝试了几次之后，选择直接进入指定路径，在文件夹里开启终端直接运行。在主机终端中输入tcpdump输错了好几次，之前就出现过这次问题，再加上h2，h3的 终端太小，一开始没有发现，还以为是L2Switch的代码出了问题，仔细一看，才发现命令没法识别，以后还要更加细心才是。除此之外，构建拓扑ping不通的问题一直困扰着我，当我用命令行构建拓扑的时候，总要尝试好几次才能ping通，不知道是不是我操作失误造成的，希望以后能够解决。