Cisco CCNA mock exam questions sample test – Question 353

.Which command(s) will enable you to configure only serial interface 0 on a Cisco router?

A. router>interface serial 0
B. router#interface serial 0
C. router(config)#interface serial 0
D. router(config-if)#interface serial 0

Correct Answer: CD

You can use either the router(config)# interface serial 0 command or the router(config-if)# interface serial 0 command to configure serial interface 0 on the router. To perform
configuration changes on a single interface, you must either enter interface configuration mode for that interface, or simply execute the command to enter configuration mode for
another interface while still at the configuration prompt for the previous interface.
Router configuration mode (as indicated by the prompt router(config)#) allows global configuration of the router. This mode, also referred to as the global configuration mode, must be
entered as a precursor to entering the interface configuration mode for a specific interface. The sequence of commands and prompts to arrive at this mode would be:
Router> enable (enters privileged mode)
Router# config t (enters global configuration mode, t is short for terminal)
Router(config)# interface serial 0 (enters interface configuration mode for the serial 0 interface)
At this point, any commands executed would be configuration changes limited to the serial 0 interface. For example, to place an address on the interface, enable the interface, and
save the configuration, the command series and prompts would be:
Router> enable
Router# config t
Router(config)# interface serial 0
Router(config-if)# ip address (addresses the interface)
Router(config-if)# no shutdown (enables or “turns on” the interface)
Router(config-if)# exit (exits global configuration mode)
Router(config)# exit (exits privileged mode)
Router# copy running-config startup config (copies the changes to the configuration file on the router)
Alternately, you could enter interface configuration mode for one interface while still in configuration mode for another interface, as shown below. After entering the interface serial 1
command, you will be editing serial 1 instead of serial 0.
Router(config)# interface serial 0
Router(config)# interface serial 1
You should not use the command router> interface serial 0. User EXEC mode, as indicated by the prompt router>, provides limited access to a router and is the initial mode you see
after authenticating to the router. The subcommand interface serial 0 is not functional before you proceed to global configuration mode and interface configuration mode for a specific
You should not use the command router# interface serial 0. Privileged mode (as indicated by the prompt router#) must be traversed to get to global configuration mode before you can
execute the subcommand interface serial 0. This subcommand is not functional while you are still in privileged mode.
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