A. To ensure the router has the correct time when generating its private/public key pairs.
B. To ensure the router has the correct time when checking certificate validity from the remote peers
C. To ensure the router time is sync with the remote peers for encryption keys generation
D. To ensure the router time is sync with the remote peers during theDH exchange
E. To ensure the router time is sync with the remote peers when generating the cookies during IKE phase 1

A. The FTP server sends back an acknowledgment （ACK） to the client
B. The FTP server allocates a port touse for the data channel and transmit that port number to the client
C. The FTP server opens the data channel to the client using the port number indicated by the client
D. The FTP client opens the data channel to the FTP server on Port 20
E. The FTP client opens the datachannel to the FTP server on Port 21