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

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

单项选择题Which statement is true?（）

A. An IPv6 address is 64 b long and is represented as hexadecimal characters.
B. An IPv6 address is 32 b long and is represented as decimal digits.
C. An IPv6 address is 128 b long and is represented as decimal digits.
D. An IPv6 address is 128 b long and is represented as hexadecimal characters.

单项选择题When upgrading the IOS image, the network administrator receives the exhibited error message. What could be the cause of this error?（）

A. The new IOS image is too large for the router flash memory.
B. The TFTP server is unreachable from the router.
C. The new IOS image is not correct for this router platform.
D. The IOS image on the TFTP server is corrupt.
E. There is not enough disk space on the TFTP server for the IOS image.

单项选择题This graphic shows the results of an attempt to open a Telnet connection to router ACCESS1 from router Remote27. Which of the following command sequences will correct this problem? （）

A. ACCESS1(config)# line console 0 ACCESS1(config-line)# password cisco
B. Remote27(config)# line console 0 Remote27(config-line)# login Remote27(config-line)# password cisco
C. ACCESS1(config)# line vty 0 4 ACCESS1(config-line)# login ACCESS1(config-line)# password cisco
D. Remote27(config)# line vty 0 4 Remote27(config-line)# login Remote27(config-line)# password cisco
E. ACCESS1(config)# enable password cisco
F. Remote27(config)# enable password cisco