Cisco CCNA OSI and TCP/IP Models Questions and Answers

Question 1

A network technician is troubleshooting an issue where a user can access local network resources but not websites on the internet. The technician suspects a problem with logical addressing. At which layer of the OSI model does this type of addressing occur?

Accepted Answer

Network Layer

Answer

The Network Layer (Layer 3) of the OSI model is responsible for logical addressing, such as IP addresses, which are used to route packets across different networks. Path determination and forwarding between networks happen at this layer. The Data Link Layer uses physical addresses (MAC addresses) for local network communication. The Transport Layer handles end-to-end communication and data segmentation, while the Application Layer provides services to end-user applications.

Question 2

Which of the following correctly identifies the Protocol Data Unit (PDU) at the OSI Transport Layer?

Accepted Answer

Segment

Answer

The Protocol Data Unit (PDU) at the Transport Layer (Layer 4) is called a segment when using TCP, or a datagram when using UDP. Packets are the PDU for the Network Layer (Layer 3), Frames are for the Data Link Layer (Layer 2), and Bits are for the Physical Layer (Layer 1).

Question 3

A web browser uses the HTTP protocol to request a webpage. In the TCP/IP model, which layer is responsible for the functions performed by the Application, Presentation, and Session layers of the OSI model?

Accepted Answer

Application Layer

Answer

The TCP/IP model's Application Layer consolidates the functions of the top three layers of the OSI model: Application, Presentation, and Session. This layer is responsible for protocols like HTTP, FTP, and SMTP that interface directly with user applications.

Question 4

During the data encapsulation process, which layer of the OSI model is responsible for adding a header that contains source and destination MAC addresses?

Accepted Answer

Data Link Layer

Answer

The Data Link Layer (Layer 2) is responsible for creating frames. During encapsulation, it adds a header containing the source and destination MAC (physical) addresses to the packet received from the Network Layer. This framing is essential for delivery on the local network segment.

Question 5

A network administrator is configuring a multilayer switch to perform routing between VLANs. This device primarily operates at which two layers of the OSI model?

Accepted Answer

Layer 2 and Layer 3

Answer

A multilayer switch, also known as a Layer 3 switch, combines the functionality of a switch and a router. It performs standard Layer 2 (Data Link) functions like MAC address-based forwarding within a VLAN, and also Layer 3 (Network) functions like IP address-based routing between different VLANs.

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Cisco CCNA OSI and TCP/IP Models Questions and Answers