What are two reasons a network administrator would use CDP?（）
A. to verify the type of cable interconnecting two devices
B. to determine the status of network services on a remote device
C. to obtain VLAN information from directly connected switches
D. to verify Layer 2 connectivity between two devices when Layer 3 fails
E. to obtain the IP address of a connected device in order to telnet to the device
F. to determine the status of the routing protocols between directly connected router
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