多项选择题
Which of the following are key characteristics of PPP?（）
A. can be used over analog circuits B. maps Layer 2 to Layer 3 address C. encapsulates several routed protocols D. supports IP only E. provides error correction
多项选择题 Which can be done to secure the virtual terminal interfaces on a router?（）
多项选择题 Which two are features of IPv6?（）
多项选择题 Which two states are the port states when RSTP has converged?（）
