CompTIA Network+ Question B-42

When troubleshooting a network problem, browsing through the log of a switch, it is discovered that multiple frames contain errors. In which of the following layers does the problem reside? (Select TWO).

A. Layer 2
B. Layer 3
C. Layer 5
D. Transport layer
E. Data link
F. Physical layer

Correct Answer: AE

Explanation:
Layer 2 of the OSI reference model is the data-link layer. Components of the data-link layer include frame-format, Media Access Control (MAC) addressing, protocol identification and error detection.
When data is being sent, it is split into protocol data units (PDUs) as it passes through the layers of the OSI model. The PDUs have different names as they are passed through the layers of the OSI model. In layer 2, the PDU is called a ‘Frame’.
The most common protocol specified in the data-link layer is Ethernet and the most common network component in the data-link layer is a network switch.
In this question, problems are discovered with Ethernet frames by examining the logs in a network switch. Therefore, for this question, we are working in Layer 2, the data-link layer.

CompTIA Network+ Question A-39

When a client calls and describes a problem with a computer not being able to reach the Internet, in which of the following places of the OSI model would a technician begin troubleshooting?

A. Transport layer
B. Physical layer
C. Network layer
D. Session layer

Correct Answer: B

Explanation:
The bottom layer of the OSI reference model is Layer 1, the physical layer.
The physical layer is the layer that defines the hardware elements of a network. These elements include:
Network Interface Cards Network topology Network cabling
The type of signals used for data transmissions
When troubleshooting a network connectivity issue, the first thing you would check is the computer’s network cabling, the network card etc. In other words, the computer’s physical connection to the network.

CompTIA Network+ Question A-29

A network engineer is dispatched to an employee office to troubleshoot an issue with the employee’s laptop. The employee is unable to connect to local and remote resources. The network engineer flips the laptop’s wireless switch on to resolve the issue. At which of the following layers of the OSI model was the issue resolved?

A. Layer 1
B. Layer 2
C. Layer 3
D. Layer 4
E. Layer 7

Correct Answer: A

Explanation:
The bottom layer of the OSI reference model is Layer 1, the physical layer.
The physical layer is the layer that defines the hardware elements of a network. These elements include:
Network Interface Cards
Network topology Network cabling
The type of signals used for data transmittions
In this question, the network engineer flipped the laptop’s wireless switch on to resolve the issue. The laptop was unable to connect to the wireless network because the wireless network interface card was switched off. Switching the wireless network interface card on enabled the laptop to connect to the wireless network. The wireless network interface card is a physical layer device.