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实验6:开源控制器实践——RYU

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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

  1. 下载虚拟机软件Oracle VisualBox或VMware;
  2. 在虚拟机中安装Ubuntu 20.04 Desktop amd64,并完整安装Mininet;

三、实验要求

(一)基本要求

  1. 完成Ryu控制器的安装。
  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。
  1. 通过Ryu的图形界面查看网络拓扑。
  1. 阅读Ryu文档的The First Application一节,运行并使用 tcpdump 验证L2Switch,分析和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,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

(二)进阶要求

  1. 阅读Ryu关于simple_switch.py和simple_switch_1x.py的实现,以simple_switch_13.py为例,完成其代码的注释工作,并回答下列问题:
# Copyright (C) 2011 Nippon Telegraph and Telephone Corporation.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
# implied.
# See the License for the specific language governing permissions and
# limitations under the License.

#导入需要使用的相应包
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
from ryu.lib.packet import ether_types


class SimpleSwitch13(app_manager.RyuApp):
    #指定OpenFlow 1.3版本
    OFP_VERSIONS = [ofproto_v1_3.OFP_VERSION] 

    def __init__(self, *args, **kwargs):
        super(SimpleSwitch13, self).__init__(*args, **kwargs)
	#self.mac_to_port是mac地址映射到转发端口的字典。
        self.mac_to_port = {} 
    @set_ev_cls(ofp_event.EventOFPSwitchFeatures, CONFIG_DISPATCHER)
    def switch_features_handler(self, ev):
        # ev.msg 是用来存储对应事件的 OpenFlow 消息类别实体
        datapath = ev.msg.datapath   
	# ofproto表示使用的OpenFlow版本所对应的ryu.ofproto.ofproto_v1_3
        ofproto = datapath.ofproto  
	# 使用对应版本的ryu.ofproto.ofproto_v1_3_parser来解析协议
        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.  The bug has been fixed in OVS v2.1.0.
        match = parser.OFPMatch()
        actions = [parser.OFPActionOutput(ofproto.OFPP_CONTROLLER,
                                          ofproto.OFPCML_NO_BUFFER)]
	# priority = 0表示优先级最低,即若所有流表都匹配不到时,才会把数据包发送到controller
        self.add_flow(datapath, 0, match, actions)
 
    # 执行 add_flow() 方法以发送 Flow Mod 消息
    def add_flow(self, datapath, priority, match, actions, buffer_id=None):
        ofproto = datapath.ofproto
        parser = datapath.ofproto_parser

        inst = [parser.OFPInstructionActions(ofproto.OFPIT_APPLY_ACTIONS,
                                             actions)]
        if buffer_id:  
            mod = parser.OFPFlowMod(datapath=datapath, buffer_id=buffer_id,
                                    priority=priority, match=match,
                                    instructions=inst)
        else:
            mod = parser.OFPFlowMod(datapath=datapath, priority=priority,
                                    match=match, instructions=inst)
        datapath.send_msg(mod)


    @set_ev_cls(ofp_event.EventOFPPacketIn, MAIN_DISPATCHER)
    # 处理PacketIn事件
    def _packet_in_handler(self, ev): 
        # If you hit this you might want to increase
        # the "miss_send_length" of your switch
        if ev.msg.msg_len < ev.msg.total_len:
            self.logger.debug("packet truncated: only %s of %s bytes",
                              ev.msg.msg_len, ev.msg.total_len)
        #从事件类里取出一些参数
	msg = ev.msg
        datapath = msg.datapath
        ofproto = datapath.ofproto
        parser = datapath.ofproto_parser
        in_port = msg.match['in_port']

        pkt = packet.Packet(msg.data)
        eth = pkt.get_protocols(ethernet.ethernet)[0]

        if eth.ethertype == ether_types.ETH_TYPE_LLDP:
	    #接受到了lldp包,就直接丢弃
            # ignore lldp packet
            return
        dst = eth.dst
        src = eth.src

        dpid = format(datapath.id, "d").zfill(16)
        self.mac_to_port.setdefault(dpid, {})

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

        #进行自学习,尽可能避免在下一次洪泛
        # learn a mac address to avoid FLOOD next time.
	#dpid是交换机的id,src是数据包的源mac地址,in_port是交换机接受到包的端口
        self.mac_to_port[dpid][src] = in_port 

        #检验目的地址是否已经学习
	if dst in self.mac_to_port[dpid]:
	#如果已经学习到,则向交换机下发流表,并让交换机向相应端口转发包
            out_port = self.mac_to_port[dpid][dst]
        else:
	#如果还没有学习到,则无法下发流表,让交换机洪泛转发包。
            out_port = ofproto.OFPP_FLOOD

        actions = [parser.OFPActionOutput(out_port)]

        # install a flow to avoid packet_in next time
        if out_port != ofproto.OFPP_FLOOD:
            match = parser.OFPMatch(in_port=in_port, eth_dst=dst, eth_src=src)
            # verify if we have a valid buffer_id, if yes avoid to send both
            # flow_mod & packet_out
            if msg.buffer_id != ofproto.OFP_NO_BUFFER:
	    #buffer_id不为None,控制器只需下发流表的命令,交换机增加了流表项后,位于缓冲区的数据包会自动转发出去。
                self.add_flow(datapath, 1, match, actions, msg.buffer_id)
                return
            else:
	    #buffer_id为None,那么控制器不仅要更改交换机的流表项,
                self.add_flow(datapath, 1, match, actions)
            #还要把数据包的信息传给交换机,让交换机把数据包转发出去。
        data = None
        if msg.buffer_id == ofproto.OFP_NO_BUFFER:
            data = msg.data
 
        out = parser.OFPPacketOut(datapath=datapath, buffer_id=msg.buffer_id,
                                  in_port=in_port, actions=actions, data=data)
        datapath.send_msg(out)

a) 代码当中的mac_to_port的作用是什么?

答:mac_to_port是mac地址映射到转发端口的字典,可用于交换机自学习。

b) simple_switch和simple_switch_13在dpid的输出上有何不同?

答:差别在于:simple_switch直接输出dpid,而simple_switch_13则在dpid前端填充0直至满16位

#simple_switch.py
        dpid = datapath.id
#################################
#simple_switch_13.py
        dpid = format(datapath.id, "d").zfill(16)

c) 相比simple_switch,simple_switch_13增加的switch_feature_handler实现了什么功能?

答:实现了交换机以特性应答消息来响应特性请求的功能

d) simple_switch_13是如何实现流规则下发的?

答:在接收到packetin事件后,首先获取包学习,交换机信息,以太网信息,协议信息等。若以太网类型是LLDP类型,则不予处理。如果不是,则获取源端口的目的端口和交换机id,先学习源地址对应的交换机的入端口,再查看是否已经学习目的mac地址,如果没有则进行洪泛转发。如果学习过该mac地址,则查看是否有buffer_id,如果有的话,则在添加流表信息时加上buffer_id,向交换机发送流表。

e) switch_features_handler和_packet_in_handler两个事件在发送流规则的优先级上有何不同?

答:switch_features_handler下发流表的优先级比_packet_in_handler的优先级高。

实验心得

标签:控制器,ryu,datapath,id,msg,开源,ofproto,RYU,port
来源: https://www.cnblogs.com/031902522ycy/p/15427259.html