實驗6：開源控制器實踐——RYU

一、實驗目的

• 能夠獨立部署RYU控制器；
• 能夠理解RYU控制器實現軟體定義的集線器原理；
• 能夠理解RYU控制器實現軟體定義的交換機原理。

二、實驗環境

• 下載虛擬機器軟體Oracle VisualBox或VMware；
• 在虛擬機器中安裝Ubuntu 20.04 Desktop amd64，並完整安裝Mininet；

三、實驗要求

(一)、基本要求

• 完成Ryu控制器的安裝。
  

• 搭建下圖所示SDN拓撲，協議使用Open Flow 1.0，並連線Ryu控制器。
  

• 通過Ryu的圖形介面檢視網路拓撲。
  

• 閱讀Ryu文件的The First Application一節，執行並使用 tcpdump 驗證L2Switch，分析和POX的Hub模組有何不同。

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)
 

• h1 ping h2:
  

• h2 ping h3:
  

• 分析和POX的Hub模組有何不同:
  

二者均通過洪泛傳送報文,但是L2Swtich的下發流表不可檢視。

(二)、進階要求

閱讀Ryu關於simple_switch.py和simple_switch_1x.py的實現，以simple_switch_13.py為例，完成其程式碼的註釋工作；

# 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):
    # 定義openflow版本
    OFP_VERSIONS = [ofproto_v1_3.OFP_VERSION]
    def __init__(self, *args, **kwargs):
        super(SimpleSwitch13, self).__init__(*args, **kwargs)
        # 定義儲存mac地址到埠的一個對映
        self.mac_to_port = {}
    # 處理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：流表項匹配，OFPMatch()：不匹配任何資訊
        actions = [parser.OFPActionOutput(ofproto.OFPP_CONTROLLER,
                                          ofproto.OFPCML_NO_BUFFER)]
        self.add_flow(datapath, 0, match, actions)#新增流表項
    # 新增流表函式
    def add_flow(self, datapath, priority, match, actions, buffer_id=None):
        # 獲取交換機資訊
        ofproto = datapath.ofproto
        parser = datapath.ofproto_parser
        # 對action進行包裝
        inst = [parser.OFPInstructionActions(ofproto.OFPIT_APPLY_ACTIONS,
                                             actions)]
        # 判斷是否有buffer_id，生成mod物件
        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)
        # 傳送mod
        datapath.send_msg(mod)
    # 觸發packet in事件時，呼叫_packet_in_handler函式
    @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)
        # 獲取包資訊，交換機資訊，協議等等
        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型別
        if eth.ethertype == ether_types.ETH_TYPE_LLDP:
            # ignore lldp packet
            return
        # 獲取源埠，目的埠
        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)
        # 學習包的源地址，和交換機上的入埠繫結
        # learn a mac address to avoid FLOOD next time.
        self.mac_to_port[dpid][src] = in_port
        # 檢視是否已經學習過該目的mac地址
        if dst in self.mac_to_port[dpid]:
            out_port = self.mac_to_port[dpid][dst]
        # 否則進行洪泛
        else:
            out_port = ofproto.OFPP_FLOOD
        actions = [parser.OFPActionOutput(out_port)]
        # 下發流表處理後續包，不再觸發 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
		# 傳送Packet_out資料包
        out = parser.OFPPacketOut(datapath=datapath, buffer_id=msg.buffer_id,
                                  in_port=in_port, actions=actions, data=data)
        # 傳送流表
        datapath.send_msg(out) 
 

• 回答以下問題：

1. 程式碼當中的mac_to_port的作用是什麼？
   答：儲存mac地址到交換機埠的對映，為交換機自學習功能提供資料結構進行mac埠的儲存
2. simple_switch和simple_switch_13在dpid的輸出上有何不同？
   答：在simple_switch_13中，會在前端加上0以填充至16位，simple_switch直接輸出dpid
3. 相比simple_switch，simple_switch_13增加的switch_feature_handler實現了什麼功能？
   答：實現了交換機以特性應答訊息響應特性請求
4. simple_switch_13是如何實現流規則下發的？
   答：在接收到packetin事件後，首先獲取包學習，交換機資訊，乙太網資訊，協議資訊等。如果乙太網型別是LLDP型別，則不予處理。如果不是，則獲取源埠目的埠，以及交換機id，先學習源地址對應的交換機的入埠，再檢視是否已經學習目的mac地址，如果沒有則進行洪泛轉發。如果學習過該mac地址，則檢視是否有buffer_id，如果有的話，則在新增流動作時加上buffer_id，向交換機發送流表
5. switch_features_handler和_packet_in_handler兩個事件在傳送流規則的優先順序上有何不同？
   答：switch_features_handler下發流表的優先順序更高

四、個人總結

（一）、遇到的問題

• 首先是安裝完ryu後不能建立拓撲，應該是python版本的問題，但我簡單粗暴的重新安裝了一下mininet。
  
• 一開始執行gui_topology.py時提示no module name，後面發現是在因為在ryu資料夾下開啟的終端，只需要返回031902426目錄下執行即可。
• 建立拓撲後無法ping通，重新啟用ryu控制器，再使用Ryu驗證L2Switch，最後建立拓撲。
  

(二)、實驗總結

• 通過本次實驗瞭解了開源軟體Ryu控制器的相關操作，能夠獨立部署RYU控制器；能夠理解RYU控制器實現軟體定義的集線器原理；能夠理解RYU控制器實現軟體定義的交換機原理。