实验6：开源控制器实践——RYU

基本要求

• 分析L2Switch和POX的Hub模块有何不同

Ryu的L2Switch模块和POX的Hub模块都采用洪泛转发的方式，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。

• 修改过的L2032002234.py代码

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)

• 体现和验证修改的截图
  

个人总结

• 实验难度：
  本次的实验难度基本要求部分难度不大，只需要按照课件一步一步进行即可。
• 实验过程遇到的困难及解决办法:
  困难：在搭建好拓扑的时候，运行ryu后，发现pingall全都ping不通。
  解决办法：在分析后得知，应该先执行命令ryu-manager L2Switch.py运行 ryu，再建立拓扑。
  困难：修改模块的时候发现程序运行错误。
  解决办法：发现有些方法使用错误，参考同学的修正。
• 个人感想：
  通过本次的实验，我明白了ryu与pox转发的流表的区别，pox是直接向交换机发送流表项的，因此可以直接查看交换机流表项，而ryu要经过处理packet_in事件后，才向交换机下发流表。