实验6：开源控制器实践——RYU

一、基础要求

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，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。

h1 ping h2

h1 ping h3

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）

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)

查看流表

二、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：

 # 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]	 # OpenFlow1.3版本

    def __init__(self, *args, **kwargs):
        super(SimpleSwitch13, self).__init__(*args, **kwargs)
        self.mac_to_port = {}	# 保存(交换机id, mac地址)到转发端口的字典

	# 处理SwitchFeatures事件
    @set_ev_cls(ofp_event.EventOFPSwitchFeatures, CONFIG_DISPATCHER)
    def switch_features_handler(self, ev):
        datapath = ev.msg.datapath	# 存储交换机的信息
        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，这里OFPMatch()指不匹配任何信息
        actions = [parser.OFPActionOutput(ofproto.OFPP_CONTROLLER,
                                          ofproto.OFPCML_NO_BUFFER)]	# actions是动作，表示匹配成功不缓存数据包并发送给控制器
        self.add_flow(datapath, 0, match, actions)	# add_flow是添加流表项的函数,我们可以从add_flow的函数中看到其调用了send_msg(mod),因此本函数的目的即为下发流表。

	# 增加流表项
    def add_flow(self, datapath, priority, match, actions, buffer_id=None):
        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)
        else:
            mod = parser.OFPFlowMod(datapath=datapath, priority=priority,
                                    match=match, instructions=inst)
        datapath.send_msg(mod)
        
        
	# 说明控制器在MAIN_DISPATCHER状态并且触发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:		# 传输出错，打印debug信息
            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	# 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)

        # learn a mac address to avoid FLOOD next time.
        self.mac_to_port[dpid][src] = in_port		# 交换机自学习，取来往数据包的交换机id、源mac和入端口绑定来构造表。

	# 查看是否已经学习过该目的mac地址
        if dst in self.mac_to_port[dpid]:	# 若在表中找到出端口信息，指示出端口
            out_port = self.mac_to_port[dpid][dst]
        # 否则，洪泛    
        else:
            out_port = ofproto.OFPP_FLOOD

        actions = [parser.OFPActionOutput(out_port)]

        # 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:	# 有buffer_id，带上buffer_id，然后只发送Flow_mod报文，因为交换机已经有缓存数据包，就不需要发送packet_out报文
                self.add_flow(datapath, 1, match, actions, msg.buffer_id)
                return
            else:
                self.add_flow(datapath, 1, match, actions)	# 若没有buffer_id，发送的Flow_Mod报文就无需要带上buffer_id，但是下一步要再发送一个Packet_out报文带上原数据包信息。
        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)

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

2.编程实现和ODL实验的一样的硬超时功能。

# 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)`

个人总结

本次实验遇到的问题比较多，基础部分在查看流表时由于构建mininet拓扑网络时使用的是OpenFlow13（用OpenFlow10时，报错如下图），因此查看流表报错
s1.mgmt: version negotiation failed (we support version 0x01, peer supports version 0x04) ovs-ofctl: s1: failed to connect to socket (Broken pipe)

解决方法
https://www.cnblogs.com/fjlinww/p/10753160.html
本次的进阶要求总的来说比较难，做的时间也比较久，特别是源码的注释，查阅了很多资料才完成，但是对于我的提升还是蛮大的，另外通过这次实践我学会了独立部署RYU控制器，理解了RYU控制器实现软件定义的集线器原理，对于ryu有了更多的了解。