CISSP Match each OSI layer to its function. Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✓

  Transport: Provides reliable data transfer and flow control

  Why this is correct

  The Transport layer is crucial for establishing and maintaining end-to-end communication between applications on different hosts. It ensures reliable data transfer through mechanisms like segmentation, reassembly, sequencing, acknowledgments, and retransmission of lost or corrupted data segments. Furthermore, it implements flow control to prevent a fast sender from overwhelming a slower receiver, optimizing data delivery efficiency and integrity.

• ✓

  Network: Routes packets using logical addressing

  Why this is correct

  The Network layer is fundamentally responsible for routing packets across different networks, enabling internetwork communication. It achieves this by utilizing logical addressing schemes, such as IP addresses, to uniquely identify hosts and networks. Routers operate at this layer, making intelligent forwarding decisions based on these logical addresses to determine the optimal path for data packets from the source to the ultimate destination.

• ✓

  Data Link: Transfers frames between directly connected nodes

  Why this is correct

  The Data Link layer manages the transfer of data frames between directly connected network nodes within the same local network segment. It handles physical addressing (e.g., MAC addresses) for local delivery, performs error detection on transmitted frames to ensure data integrity over the link, and controls access to the shared physical medium. This layer ensures reliable communication over a single network hop.

• ✓

  Physical: Transmits raw bits over physical medium

  Why this is correct

  The Physical layer is concerned with the actual transmission of raw bit streams over the physical communication medium. This includes defining electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating physical links. It dictates aspects such as voltage levels, data rates, cable types, connectors, and signal encoding, ensuring the physical transfer of unstructured data bits.

• ✗

  Transport: Routes packets using logical addressing

  Why it's wrong here

  This statement is incorrect because routing packets using logical addressing is a core function of the Network layer, not the Transport layer. The Transport layer focuses on providing reliable, end-to-end communication between specific applications (processes) on hosts, using port numbers, rather than determining the path for data across multiple network segments. Its role is process-to-process delivery, not host-to-host pathfinding.

• ✗

  Network: Provides reliable data transfer

  Why it's wrong here

  This statement is incorrect because providing reliable data transfer is a primary function of the Transport layer, not the Network layer. The Network layer, particularly with protocols like IP, typically offers a best-effort, connectionless service, meaning it does not guarantee delivery, sequencing, or error recovery for individual packets. Reliability mechanisms, such as acknowledgments and retransmissions, are implemented at the Transport layer to ensure data integrity and completeness.

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