After issuing the show interfaces terse command, you notice that the status of one interface is "up down". What does this indicate?"()A.Layer 1 on the interface is up but Layer 2 is down.B.Layer 2 on the interface is up but Layer 3 has not been configured

A.是down的，需要通过undo shutdown命令开启;

B.任何时候都是up的，除非使用shutdown命令关闭;

C.up或down要依据其subvlan中是否包含物理端口，subvlan中包含物理端口时，该虚接口就up;否则就是down的;

D.以上都不对。

Routers R1 and R2, OSPF neighbors in area 0 over their Fa0/0 interfaces (respectively), currently both successfully use OSPF MD5 authentication. The OSPF configuration includes the area 0 authentication command under the router ospf 1 command.Which of the following commands must have been configur ed on R1‘s Fa0/0 interface?（）

A. ip ospf authentication null

B. ip ospf authentication message - digest

C. ip ospf authentication -key whatever- it - is

D. ip ospf message - digest - key 1 md5 whatever - it - is

E. ip ospf md5 1 key whatever - it - is

A.当主接口由up转为down后，立即切换到备份接口。

B.当主接口由down转为up后，立即切换回主接口。

C.当主接口由up转为down后，等待一定时间后，若主接口状态仍为down，才切换到备份接口。

D.当主接口由down转为up后，等待一定时间后，若主接口状态仍为up，才切换回主接口。

下面哪种说法正确? ()

A、当主接口由up 转为down 后,立即切换到备份接口。

B、当主接口由down 转为up 后,立即切换回主接口。

C、当主接口由up 转为down 后,等待一定时间后,若主接口状态仍为down,才切换到备份接口。

D、当主接口由down 转为up 后,等待一定时间后,若主接口状态仍为up,才切换回主接口。