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。

h1 ping h2

h1 ping h3

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)

查看流表