Quick Kit: 38 MCQs with answers

Network

Layer 3 (Network) handles IP addresses and routing. Routers operate at this layer.

Data Link

Layer 2 (Data Link) uses MAC addresses and frames. Switches and bridges work here.

Segment

TCP uses segments at Layer 4. UDP uses datagrams.

Presentation

Layer 6 (Presentation) translates data formats, handles encryption, compression, and character encoding.

Headers are added at each layer

Encapsulation adds headers (and sometimes trailers) as data moves down the layers. Decapsulation removes them on the receiver side.

Layer 3 (Network)

After verifying physical connectivity (Layer 1), the next step is to check logical addressing and routing at Layer 3 (Network).

The OSI model is a 7-layer reference model, while TCP/IP is a 4-layer protocol suite used on the internet

The OSI model is a conceptual 7-layer framework. TCP/IP is a practical 4-layer protocol suite that powers the internet. They are not competitors; OSI helps think abstractly, TCP/IP is what is actually used.

Layer 2 (Data Link)

Switches operate at Layer 2 (Data Link), using MAC addresses to forward frames.

Session

Layer 5 (Session) manages dialogues between applications, including session control (setup, maintenance, teardown).

True

The International Organization for Standardization (ISO) developed the OSI model in 1984.

False

Each layer communicates logically with its peer layer, but physically data flows through adjacent layers (down on sender, up on receiver).

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Encapsulation adds headers/trailers at each layer. Decapsulation removes them on the receiver side.

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The Data Link layer uses frames as its PDU, which include MAC addresses.

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Full marks require the correct order starting from Layer 7 down to Layer 1.

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Focus on raw bit transmission and physical hardware.

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Mention MAC addresses, frames, and error detection.

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Include IP addressing, routing, and routers.

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Give examples like HTTP and SMTP.

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Switch for Layer 2, router for Layer 3.

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Contrast reliability, connection orientation, and error recovery.

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Focus on session management and control.

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Mention translation, encryption, compression, and encoding.

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Describe the downward movement and header addition.

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Describe the upward movement and header removal.

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Define PDU and list the correct terms for each layer.

Layer 3 (Network layer), because logical addressing and routing determine the path to a different subnet.

Since the devices are on the same subnet (they communicate via the switch at Layer 2), but cannot reach a server on a different subnet, the problem lies in inter-network communication. Layer 3 (Network layer) is responsible for logical addressing (IP addresses) and routing, which are required to forward packets across…

At Layer 4, the PDU is a segment (with TCP or UDP header); at Layer 2, the PDU is a frame (with MAC addresses and a trailer).

In the OSI model, the Transport layer (Layer 4) encapsulates data into segments (for TCP) or datagrams (for UDP), adding a header with port numbers. The Data Link layer (Layer 2) encapsulates the packet from Layer 3 into a frame, adding MAC addresses and a trailer for error detection. The other options incorrectly mix…

Both Layer 2 and Layer 3, because it uses IP addresses for routing and MAC addresses for frame delivery.

The device makes forwarding decisions based on IP addresses (Layer 3 function) and rewrites MAC addresses when forwarding between segments (Layer 2 function). This describes a router or a Layer 3 switch, which operates at both the Network layer (routing) and the Data Link layer (frame handling). The device does not ins…

Layer 4 (Transport) ensures reliable delivery; Layer 1 (Physical) handles the physical medium.

The Transport layer (Layer 4) provides reliable delivery through protocols like TCP, which manages sequencing, acknowledgments, and retransmissions. The Physical layer (Layer 1) is responsible for transmitting raw bits over the physical medium, whether copper or fiber. The Data Link layer (Layer 2) handles framing and…

Layer 6 (Presentation), because it is responsible for translating between different data formats and character encodings.

The Presentation layer (Layer 6) handles data translation, including character encoding conversion (e.g., ASCII to EBCDIC), encryption, and compression. The Application layer (Layer 7) provides network services to user applications but does not typically perform encoding translation. The Session layer manages connectio…

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Describe the bottom-up approach and give an example.

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Emphasize the 'what' vs. 'how' distinction and the common vocabulary.

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Contrast IP (logical, hierarchical) with MAC (physical, flat).

Layer 1 (Physical) and Layer 2 (Data Link) — because bit errors originate at Layer 1, and Layer 2's error detection (e.g., CRC) may be disabled or not configured to trigger retransmission.

Bit errors originate at Layer 1 (Physical) due to signal degradation. Layer 2 (Data Link) typically uses a frame check sequence (e.g., CRC) to detect errors, but it does not inherently request retransmission; that is often left to higher layers (e.g., Layer 4 TCP). If the application never requests retransmission, it m…

Layer 3 (Network) for IP forwarding, Layer 2 (Data Link) for MAC rewriting, and Layer 6 (Presentation) for encryption.

The appliance makes forwarding decisions based on IP addresses, which is a Layer 3 function. Rewriting MAC addresses when forwarding between VLANs is a Layer 2 function (since MAC addresses are used at the Data Link layer). Encryption of payload is a Layer 6 (Presentation) function, as it involves transforming data for…

Layer 4 (Transport) ensures reliable data transfer via TCP; Layer 1 (Physical) handles the physical medium differences by defining electrical/optical signals and connectors.

Reliable data transfer with guaranteed delivery and ordering is a function of Layer 4 (Transport), specifically using TCP which provides acknowledgments, retransmissions, and sequencing. Physical medium differences (copper vs. fiber) are handled at Layer 1 (Physical), which defines the electrical/optical characteristic…

Layer 6 (Presentation) — because this layer is responsible for translating between different data formats, including character encoding.

The Presentation layer (Layer 6) is explicitly responsible for data translation, including character encoding conversion (e.g., ASCII to EBCDIC), encryption, and compression. The Application layer (Layer 7) provides network services to applications but does not typically handle low-level encoding translation; that is t…

Layer 3 (Network) — the most likely issue is incorrect IP routing configuration, such as a missing default gateway or incorrect routing table entries.

Since the devices can communicate within the same subnet (Layer 2 works), but cannot reach a server on a different subnet, the problem is likely at Layer 3 (Network), which handles logical addressing and routing. The devices need to forward packets to a router (default gateway) to reach the other subnet. A missing or m…