实验6:开源控制器实践——RYU

一、实验目的

  • 能够独立部署RYU控制器;
  • 能够理解RYU控制器实现软件定义的集线器原理;
  • 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。

  1. 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。
点击查看代码
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)



L2Switch和POX的Hub模块的不同:

  • 相同之处在于: 二者实现的都是洪泛发送ICMP报文,所以在h1去pingh2时,h2和h3可以看到都有抓到数据包。
  • 不同之处在于:Ryu中L2Switch下发的流表是无法查看的,而POX中Hub模块可以查看。
  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)

(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:
点击查看代码
# 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.

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): #继承了ryu.base.app_manager
    OFP_VERSIONS = [ofproto_v1_3.OFP_VERSION] #OFP_VERSIONS指OpenFlow版本,这里调取了在ofproto_v1_3.py里声明的静态变量OFP_VERSION,值为4,为OpenFlow1.3版本。

    def __init__(self, *args, **kwargs):
        super(SimpleSwitch13, self).__init__(*args, **kwargs)
        self.mac_to_port = {}  #self.mac_to_port是一个保存(交换机id, mac地址)到转发端口的字典。


	#这里是利用了一个装饰器实现了对事件的控制。
  	#控制器事件(Event),Event具体见ryu/controller/ofp_event.py,其事件名称是由接收到的报文类型来命名的,名字为Event+报文类型,例如本例中,控制器收到的是交换机发送的FEATURE_REPLY	报文,所以事件名称为EventOFPSwitchFeatures。所以本事件其实就是当控制器接收到FEATURE_REPLY报文触发。
  	#控制器状态:ryu控制器和交换机交互有4个阶段,详见ryu/ryu/controller/handler.py
    @set_ev_cls(ofp_event.EventOFPSwitchFeatures, CONFIG_DISPATCHER)
    def switch_features_handler(self, ev):
        datapath = ev.msg.datapath  #datapath存储交换机的信息
        ofproto = datapath.ofproto
        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() #match指流表项匹配,这里OFPMatch()指不匹配任何信息
        actions = [parser.OFPActionOutput(ofproto.OFPP_CONTROLLER,
                                          ofproto.OFPCML_NO_BUFFER)] #actions是动作,表示匹配成功不缓存数据包并发送给控制器
        self.add_flow(datapath, 0, match, actions) #add_flow是添加流表项的函数,我们可以从add_flow的函数中看到其调用了send_msg(mod),因此本函数的目的即为下发流表。


	 #add_flow()函数作用是增加流表项;
	  #参数有datapath,优先级,匹配项,动作,buffer_id;
          #此流表项匹配成功后应立即执行所规定的动作。如果此函数参数有buffer_id(就是交换机发送来的数据包有buffer_id,即交换机有缓存),那发送的Flow_Mod报文就带上buffer_id,若没有buffer_id,buffer_id就是None。最后,发出Flow_Mod报文
    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)
        
	#说明控制器在MAIN_DISPATCHER状态并且触发Packet_In事件时调用_packet_in_handler函数
    @set_ev_cls(ofp_event.EventOFPPacketIn, MAIN_DISPATCHER)
    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: #传输出错,打印debug信息
            self.logger.debug("packet truncated: only %s of %s bytes",
                              ev.msg.msg_len, ev.msg.total_len)
        #这里是从接收到的Packet_In报文中取出各种信息,如果报文是lldp报文,忽略它。随后用此dpid(交换机id)初始化mac_to_port,并在日志打印此Packet_In的基本信息。       
        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:
            # 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)

        # learn a mac address to avoid FLOOD next time.
        self.mac_to_port[dpid][src] = in_port #交换机自学习,取来往数据包的交换机id、源mac和入端口绑定来构造表。

        if dst in self.mac_to_port[dpid]: #若在表中找到出端口信息,指示出端口
            out_port = self.mac_to_port[dpid][dst]
        else:
            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:#有buffer_id,带上buffer_id,然后只发送Flow_mod报文,因为交换机已经有缓存数据包,就不需要发送packet_out报文
                self.add_flow(datapath, 1, match, actions, msg.buffer_id)#add_flow函数内部就已发送了Flow_mod报文。,后面不用send_msg()
                return
            else:
                self.add_flow(datapath, 1, match, actions)#若没有buffer_id,发送的Flow_Mod报文就无需要带上buffer_id,但是下一步要再发送一个Packet_out报文带上原数据包信息。
        data = None
        if msg.buffer_id == ofproto.OFP_NO_BUFFER:
            data = msg.data
	#发送Packet_out数据包 带上交换机发来的数据包的信息
        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?
  • 保存mac地址到交换机端口的映射
b) simple_switch和simple_switch_13在dpid的输出上有何不同?
simple_switch
dpid = datapath.id
self.mac_to_port.setdefault(dpid, {})
self.logger.info("packet in %s %s %s %s", dpid, src, dst, msg.in_port)
simple_switch_13
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)
* simple_switch直接输出dpid,而simple_switch_13用0在dpid前填充至总长度为16
c) 相比simple_switch,simple_switch_13增加的switch_feature_handler实现了什么功能?
  • 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?
  • 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?
  • witch_features_handler下发流表的优先级比_packet_in_handler的优先级高

(三)个人总结

  • 在执行过程中出现错误:OSError: [Errno 98] Address already in use提示地址被占用

    解决办法:
    1. 使用netstat -tunlp命令,查看进程端号
    2. 杀死当前服务,在重启服务就好了
  • 经过这次实验,我学会了部署RYU控制器;能够浅浅地理解RYU控制器实现软件定义的集线器原理;能够勉强理解RYU控制器实现软件定义的交换机原理。在进阶里我看了许多代码和上网查找这些代码什么意思,让我更了解ryu的原理。
posted on 2022-10-30 23:17  时空毁灭者  阅读(53)  评论(0编辑  收藏  举报