CCNA Practice Exam Test Sample – Question 16

For what two purposes does the Ethernet protocol use physical addresses? (Choose two.)

A. to uniquely identify devices at Layer 2
B. to allow communication with devices on a different network
C. to differentiate a Layer 2 frame from a Layer 3 packet
D. to establish a priority system to determine which device gets to transmit first
E. to allow communication between different devices on the same network
F. to allow detection of a remote device when its physical address is unknown

Correct Answer: AE
Section: Operation of IP Data Networks

Explanation:
Physical addresses or MAC addresses are used to identify devices at layer 2.
MAC addresses are only used to communicate on the same network. To communicate on different network we have to use Layer 3 addresses (IP addresses) -> B is not correct.
Layer 2 frame and Layer 3 packet can be recognized via headers. Layer 3 packet also contains physical address.
On Ethernet, each frame has the same priority to transmit by default .
All devices need a physical address to identify itself. If not, they cannot communicate .