实验6:开源控制器实践——RYU

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。

  • 使用ryu --version 命令查看安装的ryu控制器版本

2.搭建下图所示SDN拓扑,协议使用Open Flow 1.0,并连接Ryu控制器。
3.通过 Ryu 的图形界面查看网络拓扑。
4.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。

  • L2Switch模块代码展示
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)
  • 利用mininet的xterm开启h1,h2,h3的命令行终端,并在h2和h3使用开启抓包(抓取eth0端口)

  • h1 ping h2

  • h1 ping h3

  • 通过dpctl dump-flows命令检查ryu的L2Switch模块和pox的Hub模块的区别

    • 在连接ryu控制器,启动L2Switch模块后查看下发流表
  • 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:

  • 代码注释
# 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.

# 引入包
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版本为1.3
    OFP_VERSIONS = [ofproto_v1_3.OFP_VERSION]

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

    # 处理EventOFPSwitchFeatures事件
    @set_ev_cls(ofp_event.EventOFPSwitchFeatures, CONFIG_DISPATCHER)
    def switch_features_handler(self, ev):
        datapath = ev.msg.datapath
        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:流表项匹配,OFPMatch():不匹配任何信息
        actions = [parser.OFPActionOutput(ofproto.OFPP_CONTROLLER,
                                        ofproto.OFPCML_NO_BUFFER)]
        self.add_flow(datapath, 0, match, actions)#添加流表项

    # 添加流表
    def add_flow(self, datapath, priority, match, actions, buffer_id=None):
        # 获取交换机信息
        ofproto = datapath.ofproto
        parser = datapath.ofproto_parser

        # 包装action 
        inst = [parser.OFPInstructionActions(ofproto.OFPIT_APPLY_ACTIONS,
                                           actions)]
        # 判断是否有buffer_id,生成相应的mod对象
        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)
        # 发送mod
        datapath.send_msg(mod)

    # 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:
            self.logger.debug("packet truncated: only %s of %s bytes",
                            ev.msg.msg_len, ev.msg.total_len)
        # 获取Packet_In报文中的各种信息:包信息,交换机信息,协议等等
        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]

        # 忽略LLDP类型
        if eth.ethertype == ether_types.ETH_TYPE_LLDP:
            # ignore lldp packet
            return

        # 获取源端口,目的端口
        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)

        # 学习包的源地址,和交换机上的入端口绑定
        # learn a mac address to avoid FLOOD next time.
        self.mac_to_port[dpid][src] = in_port

        # 在字典中查找目的mac地址是否有对应的出端口 
        if dst in self.mac_to_port[dpid]:
            out_port = self.mac_to_port[dpid][dst]
        # 没有就进行洪泛
        else:
            out_port = ofproto.OFPP_FLOOD

        actions = [parser.OFPActionOutput(out_port)]

        # 下发流表处理后续包,不再触发 packet in 事件
        # 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:
                self.add_flow(datapath, 1, match, actions, msg.buffer_id)
                return
            else:
                self.add_flow(datapath, 1, match, actions)
        data = None
        if msg.buffer_id == ofproto.OFP_NO_BUFFER:
            data = msg.data
    	# 发送Packet_out数据包
        out = parser.OFPPacketOut(datapath=datapath, buffer_id=msg.buffer_id,
                                  in_port=in_port, actions=actions, data=data)
        # 发送流表
        datapath.send_msg(out)

a) 代码当中的mac_to_port的作用是什么?

  • 答: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?

  • 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:switch_features_handler函数是新增缺失流表项到流表中,当封包没有匹配到流表时,就触发packet_in

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。

四、实验心得

1.实验难度:适中

2.实验过程遇到的困难及解决办法:

  • L2Switch模块,发现ping不通,重启之后重做了前面的部分(先开控制器)发现ping通了但是查看流表的时候并没有大家说的那样看不见流表,而实给出了流表,说明这个拓扑并没有受到L2Switch1的作用。于是我请教了舍友,发现应该先开L2Switch模块,然后再启动ryu控制器,在构建拓朴。 改正了这些错误之后就成功ping通并且也达到了查看不到流表的效果,说明成功了。

3个人感想:

  • 本次实验学会了独立部署RYU控制器,同时对RYU控制器实现软件定义的集线器原理和RYU控制器实现软件定义的交换机原理有了一些了解。
posted @ 2021-10-20 15:02  AKAJC  阅读(31)  评论(0编辑  收藏  举报