实验2：Open vSwitch虚拟交换机实践

一、实验目的

1. 能够对Open vSwitch进行基本操作；
2. 能够通过命令行终端使用OVS命令操作Open vSwitch交换机，管理流表；
3. 能够通过Mininet的Python代码运行OVS命令，控制网络拓扑中的Open vSwitch交换机

二、实验环境

Ubuntu 20.04 Desktop amd64

三、实验要求

（一）基本要求

a) /home/用户名/学号/lab2/目录下执行ovs-vsctl show命令

p0和p1连通性测试的执行结果截图

b) /home/用户名/学号/lab2/目录下开启Mininet CLI并执行pingall命令的截图

上述目录下查看OVS流表的命令结果截图

wireshark抓包截图

（二）进阶要求

阅读SDNLAB实验使用Mininet，编写Python代码，生成（一）中的SDN拓扑，并在代码中直接使用OVS命令，做到可以直接运行Python程序完成和（一）相同的VLAN划分。

代码

#!/usr/bin/python
 
from mininet.net import Mininet
from mininet.node import Node
from mininet.link import Link
from mininet.log import  setLogLevel, info
 
def myNet():
    "Create network from scratch using Open vSwitch."
 
    info( "*** Creating nodes\n" )
    switch1 = Node( 's1', inNamespace=False )
    switch2 = Node( 's2', inNamespace=False )
 
    h1 = Node( 'h1' )
    h2 = Node( 'h2' )
    h3 = Node( 'h3' )
    h4 = Node( 'h4' )

 
    info( "*** Creating links\n" )
    Link( h1, switch1)
    Link( h2, switch1)
    Link( h3, switch2)
    Link( h4, switch2)
    Link( switch1, switch2)
 
    info( "*** Configuring hosts\n" )
    h1.setIP( '192.168.123.1/24' )
    h2.setIP( '192.168.124.1/24' )
    h3.setIP( '192.168.123.2/24' )
    h4.setIP( '192.168.124.2/24' )
       
    info( "*** Starting network using Open vSwitch\n" )
    switch1.cmd( 'ovs-vsctl del-br dp0' )
    switch1.cmd( 'ovs-vsctl add-br dp0' )

    switch2.cmd( 'ovs-vsctl del-br dp1' )
    switch2.cmd( 'ovs-vsctl add-br dp1' )


    for intf in switch1.intfs.values():
        print (intf)
        print (switch1.cmd( 'ovs-vsctl add-port dp0 %s' % intf ))


    for intf in switch2.intfs.values():
        print (intf)
        print (switch2.cmd( 'ovs-vsctl add-port dp1 %s' % intf ))
  
    # Note: controller and switch are in root namespace, and we
    # can connect via loopback interface
    #switch0.cmd( 'ovs-vsctl set-controller dp0 tcp:127.0.0.1:6633' )
     
    print (switch1.cmd(r'ovs-vsctl show'))
 
    print (switch1.cmd(r'ovs-ofctl -O OpenFlow13 add-flow dp0 priority=1,in_port=1,actions=push_vlan:0x8100,set_field:4096-\>vlan_vid,output:3'))
    print (switch1.cmd(r'ovs-ofctl -O OpenFlow13 add-flow dp0 priority=1,in_port=2,actions=push_vlan:0x8100,set_field:4097-\>vlan_vid,output:3'))
    print (switch1.cmd(r'ovs-ofctl -O OpenFlow13 add-flow dp0 priority=1,dl_vlan=0,actions=pop_vlan,output:1'))
    print (switch1.cmd(r'ovs-ofctl -O OpenFlow13 add-flow dp0 priority=1,dl_vlan=1,actions=pop_vlan,output:2'))

    print (switch2.cmd(r'ovs-ofctl -O OpenFlow13 add-flow dp1 priority=1,in_port=1,actions=push_vlan:0x8100,set_field:4096-\>vlan_vid,output:3'))
    print (switch2.cmd(r'ovs-ofctl -O OpenFlow13 add-flow dp1 priority=1,in_port=2,actions=push_vlan:0x8100,set_field:4097-\>vlan_vid,output:3'))
    print (switch2.cmd(r'ovs-ofctl -O OpenFlow13 add-flow dp1 priority=1,dl_vlan=0,actions=pop_vlan,output:1'))
    print (switch2.cmd(r'ovs-ofctl -O OpenFlow13 add-flow dp1 priority=1,dl_vlan=1,actions=pop_vlan,output:2'))



 
    #switch0.cmd('tcpdump -i s0-eth0 -U -w aaa &')
    #h0.cmd('tcpdump -i h0-eth0 -U -w aaa &')
    info( "*** Running test\n" )
    h1.cmdPrint( 'ping -c 3 ' + h3.IP() )
    h2.cmdPrint( 'ping -c 3 ' + h4.IP() )
    h1.cmdPrint( 'ping -c 3 ' + h4.IP() )
    h2.cmdPrint( 'ping -c 3 ' + h3.IP() )

 
    #print switch0.cmd( 'ovs-ofctl show dp0' )    
    #print switch0.cmd( 'ovs-ofctl dump-tables  dp0' )
    #print switch0.cmd( 'ovs-ofctl dump-ports   dp0' )
    #print switch0.cmd( 'ovs-ofctl dump-flows  dp0' )
    #print switch0.cmd( 'ovs-ofctl dump-aggregate  dp0' )
    #print switch0.cmd( 'ovs-ofctl queue-stats dp0' )
 
    info( "*** Stopping network\n" )
    switch1.cmd( 'ovs-vsctl del-br dp0' )
    switch1.deleteIntfs()
    switch2.cmd( 'ovs-vsctl del-br dp1' )
    switch2.deleteIntfs()
    info( '\n' )
 
if __name__ == '__main__':
    setLogLevel( 'info' )
    info( '*** Scratch network demo (kernel datapath)\n' )
    Mininet.init()
    myNet()

执行结果截图

个人总结

这次实验总体而言进行比较顺利，没有遇到什么太大的问题，学习掌握了ovs-vsctl相关基本操作，运用命令行下发流表，联想到了跑P4代码时在命令行下发流表和在tofino交换机下发流表，其实都是大同小异，进阶实验还学习了直接在python脚本中验证实验结果

h1.cmdPrint('ping -c 3' + h3.IP())
h2.cmdPrint('ping -c 3' + h4.IP())
h1.cmdPrint('ping -c 3' + h3.IP())
h2.cmdPrint('ping -c 3' + h4.IP())

这种方法比在命令行手敲ping命令方便的多，也更具有可移植性，直接通过h3.IP()获取到h3的IP地址，可以在未来的实验中运用这种方法来测试。

通过这两次实验，发现了python中好多与网络相关的库，都能够实现很强大的功能，有待进一步的学习。