You are attempting to add an IP address to an interface on a router with which you are unfamiliar. You type the
following command and receive the following error:
Router78(config)#interfce Serial0
^
%invalid input detected at ‘^’ marker.
Which of the following could be a reason for receiving this message?

A.
the command syntax is incorrect

B.
the interface type does not exist on this router

C.
the command is entered at the wrong prompt

D.
the interface is configured already

Explanation:
The command has a syntax error. The word interface is misspelled as indicated by the marker.
The interface type may not exist on the router, but that is not the problem with this specific error message. If
you attempt to access an interface that is not present on the router, it will elicit this same message, but the
marker will be placed at the beginning of the interface type as shown below. The interface information is in lines
14-19.
Router78(config)#interface Serial0
%invalid input detected at ‘^’ marker.
When you are unfamiliar with a router, it is best to execute the show version command, which will indicate the
type and number of interfaces on the router as shown below:

The command is not entered at the wrong prompt. It should be entered at the global configuration prompt.
If the interface were already configured, it would still allow you to access the interface and make changes.
Objective:
LAN Switching Fundamentals
Sub-Objective:
Troubleshoot interface and cable issues (collisions, errors, duplex, speed)