实验6：开源控制器实践——RYU

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。

实验要求

（一）基本要求

• 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。
  

• 建立拓扑

sudo mn --topo=single,3 --mac --controller=remote,ip=127.0.0.1,port=6633 --switch ovsk

• 连接Ryu控制器

• 通过Ryu的图形界面查看网络拓扑
  在浏览器中输入地址http://127.0.0.1:8080即可打开ryu的图形界面

• 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。

• 创建L2Switch文件并添加代码

• 运行L2Switch ryu-manager L2Switch.py

  pingall可以ping通

• 开启主机终端 mininet>xterm h2 h3

• 在h2主机终端中输入tcpdump -nn -i h2-eth0

• 在h3主机终端中输入tcpdump -nn -i h3-eth0

• h1 ping h2
  

• h1 ping h3

• 分析L2Switch和POX的Hub模块有何不同
  Hub和L2Switch模块都是洪泛转发，但L2Switch模块下发的流表无法查看，而Hub模块下发的流表可以查看
  编程修改L2Switch.py，另存为L2xxxxxxxxx.py，使之和POX的Hub模块的变得一致
• 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)

• 运行结果：
  

（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：

  a) 代码当中的mac_to_port的作用是什么？

  mac_to_port的作用是保存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？
  在simple_switch_13.py中为dpid = format(datapath.id, "d").zfill(16)
  在simple_switch.py中为dpid = datapath.id
  在simple_switch_13.py中使用了zfill() 方法返回指定长度为16的字符串，原字符串右对齐，前面填充0；而simple_switch.py直接输出dpid
  c) 相比simple_switch，simple_switch_13增加的switch_feature_handler实现了什么功能？
  增加了实现交换机以特性应答消息响应特性请求功能
  d) simple_switch_13是如何实现流规则下发的？
  在触发PacketIn事件后，首先解析相关数据结构，获取协议信息、获取源端口、包学习，交换机信息，以太网信息，等。如果以太网类型是LLDP类型，则忽略。如果不是LLDP类型，则获取目的端口和源端口还有交换机id，然后进行交换机自学习，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，如果没有就洪泛转发。如果学习过，则查看是否有buffer_id，如果有则在添加流时加上buffer_id，向交换机发送数据包和流表。
  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下发流表的优先级比_packet_in_handler高
  编程实现和ODL实验的一样的硬超时功能。

• 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.

# 引入数据包
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):
    # 定义openflow版本
    OFP_VERSIONS = [ofproto_v1_3.OFP_VERSION]

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

    # 处理SwitchFeatures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指流表项匹配，OFPMatch()指不匹配任何信息
        actions = [parser.OFPActionOutput(ofproto.OFPP_CONTROLLER,
                                          ofproto.OFPCML_NO_BUFFER)]
        self.add_flow(datapath, 0, match, actions)

    # add_flow()增加流表项
    # datapath：指定的 Switch
    # priority：此规则的优先权
    # match：此规则的 Match 条件
    # actions：动作
    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)]
        # 判断是否存在buffer_id，并生成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)
        # 发送出去
        datapath.send_msg(mod)

    # 处理PacketIn事件
    @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)
        # 解析数据结构
        msg = ev.msg    # ev.msg 是代表packet_in data structure对象
        datapath = msg.datapath
        # dp. ofproto 和 dp.ofproto_parser 是代表 Ryu 和交换机谈判的 OpenFlow 协议的对象
        # dp.ofproto and dp.ofproto_parser are objects that represent the OpenFlow protocol that Ryu and the switch negotiated
        ofproto = datapath.ofproto
        parser = datapath.ofproto_parser
        in_port = msg.match['in_port']  # 获取源端口

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

        if eth.ethertype == ether_types.ETH_TYPE_LLDP:
            # 忽略LLDP类型的数据包
            # ignore lldp packet
            return
        dst = eth.dst  # 获取目的端口
        src = eth.src  # 获取源端口

        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

        # 查看是否已经学习过该目的mac地址
        if dst in self.mac_to_port[dpid]:  # 如果目的地址存在于mac_to_port中
            out_port = self.mac_to_port[dpid][dst]
        # 否则，洪泛
        else:
            out_port = ofproto.OFPP_FLOOD  # OFPP_FLOOD标志表示应在所有端口发送数据包，即洪泛

        actions = [parser.OFPActionOutput(out_port)]

        # 下发流表避免下次触发 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)

• 代码 MyTimeOut.py

• 建立拓扑 sudo mn --topo=single,3 --mac --controller=remote,ip=127.0.0.1,port=6633 --switch ovsk

• 运行 ryu-manager MyTimeOut.py

• h1 ping h2

• 查看流表 dpctl dump-flows

个人总结

本次实验用到了 mininet 和 ryu 的相关知识。通过本次实验我更进一步的掌握了 mininet 的使用和分析，也掌握了 ryu 的基础使用。通过对比上次实验所用到的 pox 和本次实验用到的 ryu，我对 mininet 控制流表下发和硬超时有了更加深刻的理解。
遇到的问题，之前的 mininet 资源没有清空，导致可视化界面展示的与预期不符，最后使用 mm -c 清除了之前残余数据后显示正常。在使用 ryu 的时候没有保证运行的唯一性，导致配置不成功，pingall 无法 ping 通，在关闭了其他无用 ryu 端口后成功运行当前期望运行项目。
通过本次实验学到了 ryu 的基本使用方法，也加深了对 mininet 使用和原理的认知，同时也增强了我解决问题的方法。收获满满。