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Networking Concepts — Network+ practice questions

Domain 1 of the CompTIA Network+ (N10-009) exam. 207 questions on this domain in the full bank — here are four free samples with answers and explanations.

Question 1 · Difficulty 2/5

Which OSI layer is responsible for converting data into bits for transmission across the physical medium? (Select the best answer.)
  1. Layer 2. Data Link
  2. Layer 1. Physical
  3. Layer 3. Network
  4. Layer 4. Transport
Show answer & explanation

Correct answer: B

Layer 1. Physical
Layer 1 (Physical) defines the electrical, optical, and mechanical means of transmitting raw bits over a medium, it operates on the PDU called 'bits.' Layer 2 (Data Link) uses frames, not raw bit-level signaling, and handles MAC addressing and error detection. Layer 3 (Network) routes packets between networks. Layer 4 (Transport) segments data and manages end-to-end delivery using TCP or UDP.

Question 2 · Difficulty 3/5

Which OSI layer does a multilayer switch use when it makes forwarding decisions based on IP destination addresses, as opposed to its Layer 2 MAC-based forwarding behavior? (Select the best answer.)
  1. Layer 2. Data Link
  2. Layer 3. Network
  3. Layer 4. Transport
  4. Layer 5. Session
Show answer & explanation

Correct answer: B

Layer 3. Network
When a multilayer switch forwards traffic based on IP destination addresses, it operates at Layer 3 (Network), the same layer as a traditional router. Layer 2 (Data Link) forwarding uses MAC addresses and is the standard behavior of an access-layer switch consulting its MAC address table. Layer 4 (Transport) deals with port numbers and end-to-end session reliability, some advanced devices perform Layer 4 inspection, but IP-based forwarding is definitively Layer 3. Layer 5 (Session) manages dialog control and synchronization between applications, not packet forwarding.

Question 3 · Difficulty 2/5

Which OSI layer is responsible for establishing, managing, and terminating communication sessions between two applications? (Select the best answer.)
  1. Layer 4. Transport
  2. Layer 6. Presentation
  3. Layer 5. Session
  4. Layer 7. Application
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Correct answer: C

Layer 5. Session
Layer 5 (Session) is responsible for establishing, maintaining, synchronizing, and terminating sessions between communicating applications, examples include NetBIOS and RPC. Layer 4 (Transport) handles end-to-end reliable or unreliable delivery and segmentation, not session control. Layer 6 (Presentation) handles data formatting, encryption, and compression. Layer 7 (Application) provides the interface directly used by user-facing protocols such as HTTP and SMTP, not session lifecycle management.

Question 4 · Difficulty 3/5

A network analyst captures traffic and identifies a PDU that contains a source port, a destination port, a sequence number, and an acknowledgment number, but no IP addresses. At which OSI layer does this PDU exist, and what is its correct name? (Select the best answer.)
  1. Layer 2; the PDU is called a frame
  2. Layer 3; the PDU is called a packet
  3. Layer 4; the PDU is called a segment
  4. Layer 5; the PDU is called a data unit
Show answer & explanation

Correct answer: C

Layer 4; the PDU is called a segment
Source port, destination port, sequence number, and acknowledgment number are all fields defined in the TCP header, which belongs to Layer 4 (Transport); the OSI PDU at this layer is called a segment. Layer 2 PDUs are frames, which contain MAC addresses, not port numbers. Layer 3 PDUs are packets and carry IP addresses. Layer 5 (Session) does not define its own PDU name in the OSI model distinct from the layers above and below it, and it does not encapsulate the fields described.

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