1. 利用mininet创建如下拓扑，要求拓扑支持OpenFlow 1.3协议，主机名、交换机名以及端口对应正确，请给出拓扑Mininet执行结果，展示端口连接情况

　答：创建拓扑的方法有两种：一种是使用python代码编写拓扑的方式，另外一种是用miniedit创建拓扑。在本次实验中使用miniedit的方式。截图如下：

python代码如下：
from mininet.topo import Topo
class Topo2( Topo ):
def init( self ):
Topo.__init__( self )
s1 = self.addSwitch('s1')
s2 = self.addSwitch('s2')
h1 = self.addHost('h1')
h2 = self.addHost('h2')
h3 = self.addHost('h3')
h4 = self.addHost('h4')
h5 = self.addHost('h5')
h6 = self.addHost('h6')
self.addLink(h1,s1,1,1)
self.addLink(h2,s1,1,2)
self.addLink(h3,s1,1,3)
self.addLink(h4,s2,1,1)
self.addLink(h5,s2,1,2)
self.addLink(h6,s2,1,3)
self.addLink(s1,s2,4,4)
topos = { 'mytopo': ( lambda: Topo2() ) }

2. 直接在Open vSwitch下发流表，用vlan得到下列虚拟网段，请逐条说明所下发的流表含义

h1 -- h4互通
h2 -- h5互通
h3 -- h6互通
其余主机不通

答：

s1：

使用如下OVS命令实现s1接收从主机1.2.3传来的包打上vlan tag标签，并从端口4发出
sudo ovs-ofctl -O OpenFlow13 add-flow s1 priority=1,in_port=1,actions=push_vlan:0x8100,set_field:4096->vlan_vid,output:4
sudo ovs-ofctl -O OpenFlow13 add-flow s1 priority=1,in_port=2,actions=push_vlan:0x8100,set_field:4097->vlan_vid,output:4
sudo ovs-ofctl -O OpenFlow13 add-flow s1 priority=1,in_port=3,actions=push_vlan:0x8100,set_field:4098->vlan_vid,output:4
s1将接收到的数据包去除vlan tag，然后根据dl_vlan（数据包原始的vlan_id），向指定端口转发
sudo ovs-ofctl -O OpenFlow13 add-flow s1 priority=1,dl_vlan=0,actions=pop_vlan,output:1
sudo ovs-ofctl -O OpenFlow13 add-flow s1 priority=1,dl_vlan=1,actions=pop_vlan,output:2
sudo ovs-ofctl -O OpenFlow13 add-flow s1 priority=1,dl_vlan=2,actions=pop_vlan,output:3

s2：
s2将从端口号为4.5.6的主机发来的数据贴上相同的vlan tag，然后从4端口发往s1（vlan_id从0开始）
sudo ovs-ofctl -O OpenFlow13 add-flow s2 priority=1,in_port=1,actions=push_vlan:0x8100,set_field:4096->vlan_vid,output:4
sudo ovs-ofctl -O OpenFlow13 add-flow s2 priority=1,in_port=2,actions=push_vlan:0x8100,set_field:4097->vlan_vid,output:4
sudo ovs-ofctl -O OpenFlow13 add-flow s2 priority=1,in_port=3,actions=push_vlan:0x8100,set_field:4098->vlan_vid,output:4
s2将接收到的数据包去除vlan tag，然后根据dl_vlan（数据包原始的vlan_id），向指定端口转发
sudo ovs-ofctl -O OpenFlow13 add-flow s2 priority=1,dl_vlan=0,actions=pop_vlan,output:1
sudo ovs-ofctl -O OpenFlow13 add-flow s2 priority=1,dl_vlan=1,actions=pop_vlan,output:2
sudo ovs-ofctl -O OpenFlow13 add-flow s2 priority=1,dl_vlan=2,actions=pop_vlan,output:3
终端输入命令：