实验 3：Mininet 实验——测量路径的损耗率

实验 3：Mininet 实验——测量路径的损耗率

一、实验目的

在实验 2 的基础上进一步熟悉 Mininet 自定义拓扑脚本，以及与损耗率相关的设定；初步了解 Mininet 安装时自带的 POX 控制器脚本编写，测试路径损耗率。

二、实验任务

h0 向 h1 发送数据包，由于在 Mininet 脚本中设置了连接损耗率，在传输过程中会丢失一些包，本次实验的目的是展示如何通过控制器计算路径损耗速率（h0-s0-s1-h1）。这里假设控制器预先知道网络拓扑。控制器将向 s0 和 s1 发送flow_stats_request，当控制器接收到来自 s0 的 response 时，将特定流的数据包数保存在 input_pkts 中，当控制器接收到来自 s1 的 response 时，将接收到特定流的数据包数保存在 output_pkts 中，差值就是丢失的数据包数量。基于上述拓扑，编写 Mininet 脚本，设置特定的交换机间的路径损耗速率，然后编写 POX 控制器脚本，实现对路径的损耗率的测量。

三、实验步骤

1. 实验环境

安装了 Ubuntu 18.04.5 Desktop amd64 的虚拟机

2. 实验过程

SDNLAB 实验参考资料：https://www.sdnlab.com/15100.html

（1）新建并编辑 pox 脚本 flow_stats.py：

#cd pox
#touch flow_stats.py

（2）编辑文件flow_stats.py，内容如下：

#!/usr/bin/python
# Copyright 2012 William Yu
# wyu@ateneo.edu
#
# This file is part of POX.
#
# POX is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# POX is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with POX. If not, see <http://www.gnu.org/licenses/>.
#
 
"""
This is a demonstration file created to show how to obtain flow 
and port statistics from OpenFlow 1.0-enabled switches. The flow
statistics handler contains a summary of web-only traffic.
"""
 
# standard includes
from pox.core import core
from pox.lib.util import dpidToStr
import pox.openflow.libopenflow_01 as of
from pox.lib.addresses import IPAddr, EthAddr
 
# include as part of the betta branch
from pox.openflow.of_json import *
from pox.lib.recoco import Timer
import time
 
log = core.getLogger()
 
src_dpid = 0
dst_dpid = 0
input_pkts = 0
output_pkts = 0
 
def getTheTime():  #fuction to create a timestamp
  flock = time.localtime()
  then = "[%s-%s-%s" %(str(flock.tm_year),str(flock.tm_mon),str(flock.tm_mday))
  
  if int(flock.tm_hour)<10:
    hrs = "0%s" % (str(flock.tm_hour))
  else:
    hrs = str(flock.tm_hour)
  if int(flock.tm_min)<10:
    mins = "0%s" % (str(flock.tm_min))
  else:
    mins = str(flock.tm_min)
  if int(flock.tm_sec)<10:
    secs = "0%s" % (str(flock.tm_sec))
  else:
    secs = str(flock.tm_sec)
  then +="]%s.%s.%s" % (hrs,mins,secs)
  return then
 
# handler for timer function that sends the requests to all the
# switches connected to the controller.
def _timer_func ():
  for connection in core.openflow._connections.values():
    connection.send(of.ofp_stats_request(body=of.ofp_flow_stats_request()))
    connection.send(of.ofp_stats_request(body=of.ofp_port_stats_request()))
  log.debug("Sent %i flow/port stats request(s)", len(core.openflow._connections))
 
# handler to display flow statistics received in JSON format
# structure of event.stats is defined by ofp_flow_stats()
def _handle_flowstats_received (event):
   #stats = flow_stats_to_list(event.stats)
   #log.debug("FlowStatsReceived from %s: %s", dpidToStr(event.connection.dpid), stats)
   global src_dpid, dst_dpid, input_pkts, output_pkts
   #print "src_dpid=", dpidToStr(src_dpid), "dst_dpid=", dpidToStr(dst_dpid)
   for f in event.stats:
     if f.match.dl_type==0x0800 and f.match.nw_dst==IPAddr("192.168.123.2") and f.match.nw_tos==0x64 and event.connection.dpid==src_dpid: 
       #print "input: ", f.byte_count, f.packet_count
       input_pkts = f.packet_count
     if f.match.dl_type==0x0800 and f.match.nw_dst==IPAddr("192.168.123.2") and f.match.nw_tos==0x64 and event.connection.dpid==dst_dpid:
       #print "output: ", f.byte_count, f.packet_count  
       output_pkts = f.packet_count
       if input_pkts !=0:
         print getTheTime(), "Path Loss Rate =", (input_pkts-output_pkts)*1.0/input_pkts*100, "%"
 
# handler to display port statistics received in JSON format
def _handle_portstats_received (event):
   #print "\n<<<STATS-REPLY: Return PORT stats for Switch", event.connection.dpid,"at ",getTheTime()
   #for f in event.stats:
      #if int(f.port_no)<65534:
        #print "   PortNo:", f.port_no, " Fwd's Pkts:", f.tx_packets, " Fwd's Bytes:", f.tx_bytes, " Rc'd Pkts:", f.rx_packets, " Rc's Bytes:", f.rx_bytes
        #print "   PortNo:", f.port_no,  " TxDrop:", f.tx_dropped, " RxDrop:", f.rx_dropped, " TxErr:", f.tx_errors, " RxErr:", f.rx_errors, " CRC:", f.rx_crc_err, " Coll:", f.collisions 
  stats = flow_stats_to_list(event.stats)
  log.debug("PortStatsReceived from %s: %s", dpidToStr(event.connection.dpid), stats)
 
def _handle_ConnectionUp (event):
  global src_dpid, dst_dpid
  print "ConnectionUp: ", dpidToStr(event.connection.dpid)
  for m in event.connection.features.ports:
    if m.name == "s0-eth0":
      src_dpid = event.connection.dpid
    elif m.name == "s1-eth0":
      dst_dpid = event.connection.dpid
 
  msg = of.ofp_flow_mod()
  msg.priority =1
  msg.idle_timeout = 0
  msg.match.in_port =1
  msg.actions.append(of.ofp_action_output(port = of.OFPP_ALL))
  event.connection.send(msg)
 
  msg = of.ofp_flow_mod()
  msg.priority =1
  msg.idle_timeout = 0
  msg.match.in_port =2
  msg.actions.append(of.ofp_action_output(port = of.OFPP_ALL))
  event.connection.send(msg)
 
  msg = of.ofp_flow_mod()
  msg.priority =10
  msg.idle_timeout = 0
  msg.hard_timeout = 0
  msg.match.dl_type = 0x0800
  msg.match.nw_tos = 0x64


  msg.match.in_port=1
  msg.match.nw_dst = "192.168.123.2"
  msg.actions.append(of.ofp_action_output(port = 2))
  event.connection.send(msg)
 
  msg = of.ofp_flow_mod()
  msg.priority =10
  msg.idle_timeout = 0
  msg.hard_timeout = 0
  msg.match.dl_type = 0x0800
  msg.match.nw_tos = 0x64
  msg.match.nw_dst = "192.168.123.1"
  msg.actions.append(of.ofp_action_output(port = 1))
  event.connection.send(msg)
    
# main functiont to launch the module
def launch ():
  # attach handsers to listners
  core.openflow.addListenerByName("FlowStatsReceived", 
    _handle_flowstats_received) 
  core.openflow.addListenerByName("PortStatsReceived", 
    _handle_portstats_received) 
  core.openflow.addListenerByName("ConnectionUp", _handle_ConnectionUp)
 
  # timer set to execute every five seconds
  Timer(1, _timer_func, recurring=True)

现在一起看下 flowstat.py 的关键代码：

第 7 行开始，让 h0 ping h1，监测 s0 和 s1 之间的链路。如果匹配到以太网类型的包头（0x0800），并且数据包的目的 IP 地址是192.168.123.2（对照后面 Mininet 的脚本发现是 h1），并且连接到控制器的数据平面设备 id 是 s0（h0 ping h1，链路 s0-s1 上数据包是从 s0 流向 s1，s0 为源，s1 为目的地），执行 input_pkts = f.packet_count，把数据包数量i设为input_pkts；同理，如果连接到控制器的数据平面设备 id 是 s1，执行 output_pkts =f.packet_count，把数据包数量存入 output_pkts。最后求 input_pkts 和 output_pkts 的差值。一般情况下差值为正，说明链路上数据包有损耗。

（3）在装有Mininet的虚拟机里新建文件mymininet.py

#touch mymininet.py

(4) 编辑文件mymininet.py，内容如下：

参照拓扑图，新建并编辑 Mininet 脚本 mymininet3.py，控制器因为安装在本机，所以需修改参考资料代码中的控制器地址为 127.0.0.1:6633，设置 s0 和 s1 之间链路的丢包率为 0。

#!/usr/bin/python
 
from mininet.net import Mininet
from mininet.node import Node
from mininet.link import TCLink
from mininet.log import  setLogLevel, info
from threading import Timer
from mininet.util import quietRun
from time import sleep
 
def myNet(cname='controller', cargs='-v ptcp:'):
    "Create network from scratch using Open vSwitch."
    info( "*** Creating nodes\n" )
    controller = Node( 'c0', inNamespace=False )
    switch = Node( 's0', inNamespace=False )
    switch1 = Node( 's1', inNamespace=False )
    h0 = Node( 'h0' )
    h1 = Node( 'h1' )
    
    info( "*** Creating links\n" )
    linkopts0=dict(bw=100, delay='1ms', loss=0)
    linkopts1=dict(bw=100, delay='1ms', loss=0)
    link0=TCLink( h0, switch, **linkopts0)
    link1 = TCLink( switch, switch1, **linkopts1)     
    link2 = TCLink( h1, switch1, **linkopts0)
    #print link0.intf1, link0.intf2
    link0.intf2.setMAC("0:0:0:0:0:1")
    link1.intf1.setMAC("0:0:0:0:0:2")
    link1.intf2.setMAC("0:1:0:0:0:1") 
    link2.intf2.setMAC("0:1:0:0:0:2")
 
    info( "*** Configuring hosts\n" )
    h0.setIP( '192.168.123.1/24' )
    h1.setIP( '192.168.123.2/24' )
       
    info( "*** Starting network using Open vSwitch\n" )
    switch.cmd( 'ovs-vsctl del-br dp0' )
    switch.cmd( 'ovs-vsctl add-br dp0' )
    switch1.cmd( 'ovs-vsctl del-br dp1' )
    switch1.cmd( 'ovs-vsctl add-br dp1' )
 
    controller.cmd( cname + ' ' + cargs + '&' )     
    for intf in switch.intfs.values():
        print intf
        print switch.cmd( 'ovs-vsctl add-port dp0 %s' % intf )
    for intf in switch1.intfs.values():
        print intf
        print switch1.cmd( 'ovs-vsctl add-port dp1 %s' % intf )
   
    # Note: controller and switch are in root namespace, and we
    # can connect via loopback interface
    switch.cmd( 'ovs-vsctl set-controller dp0 tcp:127.0.0.1:6633' )
    switch1.cmd( 'ovs-vsctl set-controller dp1 tcp:127.0.0.1:6633' )
  
    info( '*** Waiting for switch to connect to controller' )
    while 'is_connected' not in quietRun( 'ovs-vsctl show' ):
        sleep( 1 )
        info( '.' )
    info( '\n' )
 
    #info( "*** Running test\n" )
    h0.cmdPrint( 'ping -Q 0x64 -c 20 ' + h1.IP() )
    
    sleep( 1 ) 
    info( "*** Stopping network\n" )
    controller.cmd( 'kill %' + cname )
    switch.cmd( 'ovs-vsctl del-br dp0' )
    switch.deleteIntfs()
    switch1.cmd( 'ovs-vsctl del-br dp1' )
    switch1.deleteIntfs()
    info( '\n' )
 
if __name__ == '__main__':
    setLogLevel( 'info' )
    info( '*** Scratch network demo (kernel datapath)\n' )
    Mininet.init()
    myNet()

(5)运行脚本flow_stats.py

#./pox.py flow_stats

运行后显示为

（6）运行脚本mymininet.py

#./mymininet.py

Ping 默认是每 1 秒钟测一次，ping 的结果会显示一个丢包率，这里的丢包率是根据 ping 不通的次数占总次数的百分比计算得到的。上图中由于一共 ping 了 20次，每次都能通，所以丢包率是 0。

观察 pox 侧的实时状态更新：

平均丢包率为 0，结果符合 Mininet 脚本中设置的损耗率，也有可能出现负值，可以认为没有丢包。

如果修改代码中 s0 和 s1 之间链路的丢包率为 10。

info( "*** Creating links\n" )
 linkopts0=dict(bw=100, delay='1ms', loss=0)
 linkopts1=dict(bw=100, delay='1ms', loss=10)
 link0=TCLink( h0, switch, **linkopts0)
 link1 = TCLink( switch, switch1, **linkopts1) 
 link2 = TCLink( h1, switch1, **linkopts0)