CompTIA Network+ OSI Model and Data Encapsulation Questions and Answers

Question 1

A network technician is troubleshooting an issue where a user can access local network resources but cannot browse the internet. The technician suspects a router is misconfigured. At which layer of the OSI model is the technician focusing their troubleshooting efforts?

Accepted Answer

Network Layer

Answer

The Network Layer (Layer 3) is responsible for routing data between different networks. Since the issue involves communication between the local network and the internet (an external network), the problem most likely resides at this layer where routers operate using IP addresses to forward packets.

Question 2

During the data encapsulation process, which Protocol Data Unit (PDU) is created at the Transport Layer?

Accepted Answer

Segment

Answer

At the Transport Layer (Layer 4), data from the upper layers is broken down and encapsulated into a PDU called a segment (when using TCP) or a datagram (when using UDP). This PDU includes information like port numbers for end-to-end communication.

Question 3

A web browser is preparing to send a request for a webpage. It adds an HTTP header to the user's request data. Which of the following OSI model layers is responsible for this initial step?

Accepted Answer

Application Layer

Answer

The Application Layer (Layer 7) provides the interface for applications to access network services. Protocols like HTTP (Hypertext Transfer Protocol) operate at this layer to format and exchange data for services like web browsing. Adding the HTTP header is an Application Layer function.

Question 4

Which of the following correctly describes the process of data encapsulation in the OSI model?

Accepted Answer

Each layer adds its own header to the data received from the layer above.

Answer

Data encapsulation is the process where each layer in the sending device adds its own protocol information, in the form of a header (and sometimes a trailer), to the data unit it receives from the layer above. This process happens as data moves down the OSI stack from the Application Layer to the Physical Layer.

Question 5

A network switch makes its forwarding decisions based on the MAC address contained within a specific Protocol Data Unit (PDU). What is this PDU called and at which OSI layer does it operate?

Accepted Answer

Frame, at the Data Link Layer

Answer

The Data Link Layer (Layer 2) is responsible for node-to-node data transfer on a local network. It encapsulates packets into PDUs called frames. These frames contain source and destination MAC addresses, which Layer 2 devices like switches use to forward the data to the correct device on the LAN.

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CompTIA Network+ OSI Model and Data Encapsulation Questions and Answers