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。

实验6:开源控制器实践——RYU

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。

实验6:开源控制器实践——RYU

3.通过Ryu的图形界面查看网络拓扑。

实验6:开源控制器实践——RYU

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。

  • 编写L2Switch.py代码并使用命令ryu-manager L2Switch.py运行

    • L2Switch.py代码如下:
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)
  • 运行并使用tcpdump来验证L2Switch

    • h1 ping h2

实验6:开源控制器实践——RYU

  • h1 ping h3

实验6:开源控制器实践——RYU

  • 查看流表:

实验6:开源控制器实践——RYU

  • 由以上三张截图可知,与POX的Hub模块相比的区别如下:

Hub和L2Switch都是事先洪泛转发ICMP报文,当h1 ping h2时,h1发送给h2的报文,h3也能收到,但L2Switch下发的流表为空(无法查看),而Hub模块可以查看。

(二)进阶要求

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:

  • 以下为simple_switch_13.py完整代码及注释:
# 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): #继承ryu.base.app_manager
    # 定义openflow版本
    OFP_VERSIONS = [ofproto_v1_3.OFP_VERSION]

    def __init__(self, *args, **kwargs):
        super(SimpleSwitch13, self).__init__(*args, **kwargs)
        # 定义保存mac地址到端口的一个映射
        self.mac_to_port = {}

    # 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()
        actions = [parser.OFPActionOutput(ofproto.OFPP_CONTROLLER,
                                          ofproto.OFPCML_NO_BUFFER)]
        self.add_flow(datapath, 0, match, actions)

    # 添加流表函数
    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

        # 对action进行包装
        inst = [parser.OFPInstructionActions(ofproto.OFPIT_APPLY_ACTIONS,
                                             actions)]
        # 判断是否有buffer_id,生成mod对象
        if buffer_id:
            #发送的FlowMod报文带上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)

    # 处理 packet in 事件(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
        #传输出错,打印debug信息
        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)
        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来构造表
        # learn a mac address to avoid FLOOD next time.
        self.mac_to_port[dpid][src] = in_port

        # 找该目的mac地址在表中对应的出端口信息
        if dst in self.mac_to_port[dpid]:
            out_port = self.mac_to_port[dpid][dst]
        # 无则进行洪泛
        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)
  • 回答下面问题

  • 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,为交换机自学习功能提供数据结构进行 mac-端口的存储
  • b) simple_switch和simple_switch_13在dpid的输出上有何不同?

    • simple_switch的dpid赋值语句为dpid = datapath.id,而simple_switch_13的dpid赋值语句是dpid = format(datapath.id, "d").zfill(16),很显然simple_switch是直接输出dpid,但是simple_switch_13的dpid输出是用0在dpid前填充直到总长度达到16。
  • c) 相比simple_switch,simple_switch_13增加的switch_feature_handler实现了什么功能?

    • 实现交换机以特性应答消息响应特性请求。
  • d) simple_switch_13是如何实现流规则下发的?

    • 当接收到packetin事件后,首先获取交换机信息,包学习,协议信息,以太网信息等。若以太网类型是LLDP类型,则不进行处理。若不是,则获取源端口、目的端口和交换机id,先学习源地址对应的交换机入端口,再查看是否已学习目的mac地址。若没有则进行洪泛转发,但若学习过该mac地址,则查看是否有buffer_id,若有,则在添加流动作时加上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?

    • switch_features_handler下发流表的优先级高于_packet_in_handler。

 

四、个人总结

 

  • 实验难度:较难

  • 实验过程遇到的困难及解决办法

    • 使用用Ryu的L2Switch模块下发流表,可以在窗口看到h1 ping h2 和h1 ping h3的结果(有洪泛),但是看不出来Ryu与Pox的关键区别。于是收到同学的指点使用dpctl del-flows命令查看了一下流表发现流表为空,才明白Ryu与Pox的区别。

    • 进阶要求的代码也太长了,理解容易产生偏差所以注释起来比较困难,于是参考了官方文档和同学的代码注释来解读代码。

  • 个人感想:我认为这次实验主要难度还是在进阶要求,对于基本要求由于上一次实验的试错已经对验证模块功能的操作比较熟悉了,因此在完成运行tcpdump验证L2Switch时就觉得比较得心应手了。进阶要求个人感觉对openflow协议理解有所拔高,难度大,代码注释起来困难,好在查找资料查看文档及请教同学也一点一点摸索过来,感觉还是收获蛮多的。果然老师说的我们SDN的实验作业是一年比一年难的。

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