实验6：开源控制器实践——RYU

(一)基本要求

1.搭建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。

• 建立拓扑并连接Ryu控制器
  

• 通过Ryu的图形界面查看网络拓扑
  

2.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

• 代码部分L2Switch.py

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
  

• h1 ping h3
  

• 分析L2Switch和POX的Hub模块有何不同
  连接ryu控制器，启动L2Switch模块后查看下发流表:
  

连接pox控制器，启动Hub模块后查看下发流表:

• 结论：
  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。

3.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）

• L2032002236.py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L2032002236.py并查看流表
  

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。

• 代码部分simple_switch_13.py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.

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)
        # 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()   #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:
            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    # 目的端口
        src = eth.src    # 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]:
            out_port = self.mac_to_port[dpid][dst]
        # 否则进行洪泛
        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
            # 有buffer_id，带上buffer_id，然后只发送Flow_mod报文
            if msg.buffer_id != ofproto.OFP_NO_BUFFER:
                self.add_flow(datapath, 1, match, actions, msg.buffer_id)
                return
            # 若没有buffer_id，发送的Flow_Mod报文就无需要带上buffer_id，但下一步要再发送一个Packet_out报文带上原数据包信息。
            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 带上交换机发来的数据包的信息
        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)

• 回答下列问题：
  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，可用于交换机自学习。

b)simple_switch和simple_switch_13在dpid的输出上有何不同？

simple_switch直接输出dpid,而simple_switch_13会在dpid前端加上0将其填充至16位。

c)相比simple_switch，simple_switch_13增加的switch_feature_handler实现了什么功能？

实现了交换机以特性应答消息来响应特性请求的功能.

d)simple_switch_13是如何实现流规则下发的？

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？

switch_features_handler下发流表的优先级比_packet_in_handler的优先级高。

2.编程实现和ODL实验的一样的硬超时功能

• 代码部分Timeout.py

# 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.

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):
    OFP_VERSIONS = [ofproto_v1_3.OFP_VERSION]

    def __init__(self, *args, **kwargs):
        super(SimpleSwitch13, self).__init__(*args, **kwargs)
        self.mac_to_port = {}

    @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)

    def add_flow(self, datapath, priority, match, actions, buffer_id=None, hard_timeout=0):
        ofproto = datapath.ofproto
        parser = datapath.ofproto_parser

        inst = [parser.OFPInstructionActions(ofproto.OFPIT_APPLY_ACTIONS,
                                             actions)]
        if buffer_id:
            mod = parser.OFPFlowMod(datapath=datapath, buffer_id=buffer_id,
                                    priority=priority, match=match,
                                    instructions=inst, hard_timeout=hard_timeout)
        else:
            mod = parser.OFPFlowMod(datapath=datapath, priority=priority,
                                    match=match, instructions=inst, hard_timeout=hard_timeout)
        datapath.send_msg(mod)

    @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)
        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]

        if eth.ethertype == ether_types.ETH_TYPE_LLDP:
            # ignore lldp packet
            return
        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)

        # learn a mac address to avoid FLOOD next time.
        self.mac_to_port[dpid][src] = in_port

        if dst in self.mac_to_port[dpid]:
            out_port = self.mac_to_port[dpid][dst]
        else:
            out_port = ofproto.OFPP_FLOOD

        actions = [parser.OFPActionOutput(out_port)]\

        actions_timeout=[]

        # 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
            hard_timeout=10
            if msg.buffer_id != ofproto.OFP_NO_BUFFER:
                self.add_flow(datapath, 2, match,actions_timeout, msg.buffer_id,hard_timeout=10)
                self.add_flow(datapath, 1, match, actions, msg.buffer_id)
                return
            else:
                self.add_flow(datapath, 2, match, actions_timeout, hard_timeout=10)
                self.add_flow(datapath, 1, match, actions)
        data = None
        if msg.buffer_id == ofproto.OFP_NO_BUFFER:
            data = msg.data

        out = parser.OFPPacketOut(datapath=datapath, buffer_id=msg.buffer_id,
                                  in_port=in_port, actions=actions, data=data)
        datapath.send_msg(out)

• 运行Timeout.py
  

个人总结

本次实验难度适中，总体实验的操作做起来还是挺顺利的，但实验所要回答的问题和注释需要花费较多时间查阅资料。本次实验让我了解了部署RYU控制器的方法与步骤，同时也让我了理解RYU控制器实现软件定义的集线器原理和交换机原理。
在进行本次实验过程中，也遇到了一些拦路虎，比如在运行L2032002236.py时，出现了unsupported version 0x1”. If possible, set the switch to use one of the versions [4]。的报错，在询问了已经做完的同学后，发现是openflow选择错误了，要选择1.3版本的。
其次，在回答实验问题和完成进阶要求的源码注释过程中也查阅了一些资料才了解了一些关于RYU的工作原理的知识和相关代码的作用。让我此次实验收获颇丰。