实验2：Open vSwitch虚拟交换机实践
（一）基本要求
a) /home/用户名/学号/lab2/目录下执行ovs-vsctl show命令、以及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。
代码如下：

!/usr/bin/env python

from mininet.net import Mininet
from mininet.node import Controller, RemoteController, OVSController
from mininet.node import CPULimitedHost, Host, Node
from mininet.node import OVSKernelSwitch, UserSwitch
from mininet.node import IVSSwitch
from mininet.cli import CLI
from mininet.log import setLogLevel, info
from mininet.link import TCLink, Intf
from subprocess import call

def myNetwork():

net = Mininet( topo=None,
               build=False,
               ipBase='10.0.0.0/8')

info( '*** Adding controller\n' )
c0=net.addController(name='c0',
                  controller=Controller,
                  protocol='tcp',
                  port=6633)

info( '*** Add switches\n')
s1 = net.addSwitch('s1', cls=OVSKernelSwitch)
s2 = net.addSwitch('s2', cls=OVSKernelSwitch)

info( '*** Add hosts\n')
h1 = net.addHost('h1', cls=Host, ip='10.0.0.1', defaultRoute=None)
h2 = net.addHost('h2', cls=Host, ip='10.0.0.2', defaultRoute=None)
h3 = net.addHost('h3', cls=Host, ip='10.0.0.3', defaultRoute=None)
h4 = net.addHost('h4', cls=Host, ip='10.0.0.4', defaultRoute=None)

info( '*** Add links\n')
net.addLink(s1, h1, 1, 1)
net.addLink(s1, h2, 2, 1)
net.addLink(s2, h3, 1, 1)
net.addLink(s2, h4, 2, 1)
net.addLink(s1, s2, 3, 3)

info( '*** Starting network\n')
net.build()
info( '*** Starting controllers\n')
for controller in net.controllers:
    controller.start()

info( '*** Starting switches\n')
net.get('s1').start([c0])
net.get('s2').start([c0])

info( '*** Post configure switches and hosts\n')

s1.cmd('sudo ovs-ofctl -O OpenFlow13 add-flow s1 priority=1,in_port=1,actions=push_vlan:0x8100,set_field:4096-\>vlan_vid,output:3')
s1.cmd('sudo ovs-ofctl -O OpenFlow13 add-flow s1 priority=1,in_port=2,actions=push_vlan:0x8100,set_field:4097-\>vlan_vid,output:3')
s1.cmd('sudo ovs-ofctl -O OpenFlow13 add-flow s1 priority=1,dl_vlan=0,actions=pop_vlan,output:1')
s1.cmd('sudo ovs-ofctl -O OpenFlow13 add-flow s1 priority=1,dl_vlan=1,actions=pop_vlan,output:2')
s2.cmd('sudo ovs-ofctl -O OpenFlow13 add-flow s2 priority=1,in_port=1,actions=push_vlan:0x8100,set_field:4096-\>vlan_vid,output:3')
s2.cmd('sudo ovs-ofctl -O OpenFlow13 add-flow s2 priority=1,in_port=2,actions=push_vlan:0x8100,set_field:4097-\>vlan_vid,output:3')
s2.cmd('sudo ovs-ofctl -O OpenFlow13 add-flow s2 priority=1,dl_vlan=0,actions=pop_vlan,output:1')
s2.cmd('sudo ovs-ofctl -O OpenFlow13 add-flow s2 priority=1,dl_vlan=1,actions=pop_vlan,output:2')

CLI(net)
net.stop()

if name == 'main':
setLogLevel( 'info' )
myNetwork()

个人总结
本次实验的基础要求部分，按照老师给的pdf完成问题不大。其中有遇到一些小问题在网络上也没有找到答案，通过反复尝试反复试错最后才意识到出错点。实验中涉及到了路由交换课中所学到的知识，还学会了在ubuntu中用wireshark进行抓包分析报文。