单项选择题
At which OSI layer is a logical path created between two host systems（）。
A.session B.transport C.network D.data link E.physical
多项选择题 根据下图，网络连接到路由器R2被汇总为一条192.168.176.0/21的路由，并发给R1。哪两个数据包目的地址R1会转发给R2？（）
单项选择题 What is the effect of using the service password-encryption comma（）。
单项选择题 Which protocol is an open standard protocol frame work that is commonly used in VPNs，to provid secureend-to-end communication？（）
