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
（一）基本要求
下载虚拟机软件Oracle VisualBox或VMware；
在虚拟机中安装Ubuntu 20.04 Desktop amd64，并完整安装Mininet；
三、实验要求
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。
- 在对应文件夹下执行
ryu-manager gui_topology.py --observe-links启动控制器 
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使用命令
sudo mn --topo=single,3 --mac --controller=remote,ip=127.0.0.1,port=6633 --switch ovsk,protocols=OpenFlow10搭建上述拓扑。
- 2.通过Ryu的图形界面查看网络拓扑
- 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。
L2Switch.py代码
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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_0class 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_parseractions = [ofp_parser.OFPActionOutput(ofp.OFPP_FLOOD)]
data = None
if msg.buffer_id == ofp.OFP_NO_BUFFER:
data = msg.dataout = ofp_parser.OFPPacketOut(
datapath=dp, buffer_id=msg.buffer_id, in_port=msg.in_port,
actions=actions, data = data)
dp.send_msg(out)-
- 重新构建拓扑，并对h2、h3节点进行抓包
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- 观察到h2，h3都接收到数据包
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分析和POX的Hub模块有何不同
1.查看下发流表
dpctl dump-flows2.运行ryu
ryu-manager L2Switch.py3.运行pox（Hub模块）
./pox.py log.level --DEBUG forwarding.hub无法查看L2Switch下发的流表，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（xxxxxxxxx
为学号）
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（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：
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# 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_typesclass 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)</pre>
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：simple_switch直接输出dpid，simple_switch_13会在不满16位的dpid前补0直到满16位
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。如果以太网类型是LLDP类型，则不予处理。如果不是，则获取源端口目的端口，以及交换机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？
答：switch_features_handler下发流表的优先级高于_packet_in_handler。
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实验心得
- 在本次实验中，通过阅读RYU文档并查看相关模块的源代码，了解了RYU控制器的工作原理，并比较了RYU的L2Switch模块与POX的Hub模块的异同。最开始安装RYU时，基本上根据老师的实验指导书一步一步来，即可顺利完成，而进阶部分则难度较大，尤其在阅读源码部分进度较慢。不过，虽然阅读源码的过程有些困难，但在过程中，查阅相关材料，结合源码进行阅读，也使得我对RYU的控制机制有了更加深刻的了解。
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- 观察到h2，h3都接收到数据包