A receiving host computes the checksum on a frame and determines that the frame is damaged.The frame is then discarded.At which OSI layer did this happen?（）

单项选择题Given an IP address 172.16.28.252 with a subnet mask of 255.255.240.0, what is the correct network addres?（）

A. 172.16.16.0
B. 172.16.24.0
C. 172.16.0.0
D. 172.16.28.0

单项选择题Which command can be used to verify the DLCI destination address in a Frame Relay static configuration?（）

A. show frame-relay end-to-end
B. show frame-relay map
C. show frame-relay lmi
D. show frame-relay pvc

单项选择题Which layer 2 protocol encapsulation type supports synchronous and asynchronous circuis and has built-in security mechanisms?（）

A. Frame Relay
B. HDLC
C. x.25
D. PPP

单项选择题In which circumstance are multiple copies of the same unicast frame likely to be transmitted in a switched LAN?（）

A. after broken links are re-established
B. in an improperly implemented redundant topology
C. when upper-layer protocols require high reliability
D. during high traffic periods
E. when a dual ring topology is in use

单项选择题Which command sets and automatically encrypts the privileged enable mode password?（）

A. enbale password c1sco
B. secret enable c1sco
C. password enable c1sco
D. enable secret c1sco