单项选择题
A. Layer 2
B. Layer 3
C. Layer 4
D. Layer 5
E. Layer 6
F. Layer 7
单项选择题 In the "host to host" layer of the DOD model, which of the following is a valid connection oriented protocol?（）
单项选择题 In which of the following scenarios would the "show cdp neighbors detail"command be an appropriate troubleshooting tool?（）
单项选择题 Which command can be used to determine the type of cable attached to the Serial 0/0 interface on a router?（）