解决一个坑爹的mininet的pingall失败的问题(自己编译安装openvswitch后)

我在Ubuntu16.04上装好mininet和opendaylight后是可以正常运行的：

root@mininet-vm [07:45:54 PM] [/etc/apt] 
-> # mn --controller=remote,ip=192.168.179.129,port=6633 --topo=tree,2
*** Creating network
*** Adding controller
*** Adding hosts:
h1 h2 h3 h4 
*** Adding switches:
s1 s2 s3 
*** Adding links:
(s1, s2) (s1, s3) (s2, h1) (s2, h2) (s3, h3) (s3, h4) 
*** Configuring hosts
h1 h2 h3 h4 
*** Starting controller
c0 
*** Starting 3 switches
s1 s2 s3 ...
*** Starting CLI:
mininet> pingall
*** Ping: testing ping reachability
h1 -> X h3 h4 
h2 -> h1 h3 h4 
h3 -> h1 h2 h4 
h4 -> h1 h2 h3 
*** Results: 8% dropped (11/12 received)
mininet> pingall
*** Ping: testing ping reachability
h1 -> h2 h3 h4 
h2 -> h1 h3 h4 
h3 -> h1 h2 h4 
h4 -> h1 h2 h3 
*** Results: 0% dropped (12/12 received)

但当我自己编译安装openvswitch后，遇到了问题:

mininet> pingall
*** Ping: testing ping reachability
h1 -> X X X
h2 -> X X X
h3 -> X X X
h4 -> X X X
*** Results: 100% dropped (0/12 received)

我始终找不到问题出在哪里，在网上查阅了 很多资料后，在下面看到了一个让我眼前一亮的回答：
New to SDN - Mininet with HP VAN SDN 2.7 - Pings f… - Hewlett Packard Enterprise Community
里面提到的指定mininet参数–switch ovs,protocols=OpenFlow10让我有了想法

root@mininet-vm [07:45:54 PM] [/etc/apt] 
-> # mn --controller=remote,ip=192.168.179.129,port=6633 --topo=tree,2 --switch ovs,protocols=OpenFlow10
*** Creating network
*** Adding controller
*** Adding hosts:
h1 h2 h3 h4 
*** Adding switches:
s1 s2 s3 
*** Adding links:
(s1, s2) (s1, s3) (s2, h1) (s2, h2) (s3, h3) (s3, h4) 
*** Configuring hosts
h1 h2 h3 h4 
*** Starting controller
c0 
*** Starting 3 switches
s1 s2 s3 ...
*** Starting CLI:
mininet> pingall
*** Ping: testing ping reachability
h1 -> X h3 h4 
h2 -> h1 h3 h4 
h3 -> h1 h2 h4 
h4 -> h1 h2 h3 
*** Results: 8% dropped (11/12 received)

果真，指定了参数后就能用了，吐血啊