集线器、交换机、路由器、中继器及网关、网桥之间的区别
http://blog.csdn.net/lx85416281/article/details/53234154
点到点通信和端到端通信
https://www.zhihu.com/question/49245486
http://bestkuan.blog.51cto.com/939332/212008/
减脂运动
https://www.zhihu.com/question/27987054