实验三：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 16.04.5 Desktop amd64 的虚拟机实验过程。

2.实验过程

1.若pox被锁则输入：

sudo chmod 777 pox

2 利用sudo gedit编辑文件

新建并编辑 pox 脚本 flowstat.py：

在 pox 安装目录下（Mininet 完整安装包含了 pox）执行以下命令运行 pox 脚本

$ ./pox.py

脚本代码如下：

#!/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 "
<<<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)

结果如图：

代码解释：

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，把数据包数量存入

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 编辑 Mininet 脚本 mymininet3.py

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。

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' )

设置 s0 和 s1 之间链路的丢包率为 0

info( " Creating links
" )
 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)

再执行命令运行 Mininet 脚本 mymininet3.py

$ sudo python mymininet3.py

结果如下：

解释：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
" )
 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)

重新运行 Mininet 脚本 mymininet3.py，20 秒时间的 ping 过程中有 icmp_seq 为2/4/14/16/19/20 共 6 次 ping 不通，所以丢包率计算为 30%。

结果如下：

POX 端重新测试，会发现出现丢包现象，但是实际测量出的丢包率会有浮动，链路的性能总体受到了限制。

四、心得体会

一开始做实验的时候，丢包率一直为0。