ISC2 CC Network Security Practice Question
Which layer of the OSI model is responsible for routing packets based on IP addresses?
⚠ Common exam trap
A common mix-up: candidates confuse the roles of Layer 2 and Layer 3: candidates often associate 'packets' with the Data Link layer because both deal with addressing, but only Layer 3 uses IP addresses for routing across networks.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
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Network layer
The Network layer (Layer 3) is responsible for logical addressing and routing packets based on IP addresses. It determines the best path for data to travel across multiple networks, using routers to forward packets hop-by-hop. This layer encapsulates data into packets and handles fragmentation and reassembly when necessary.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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Data Link layer
Why it's wrong here
The Data Link layer handles MAC addressing, framing and error detection on the local segment; it forwards frames within one broadcast domain and does not inspect IP addresses for path selection. It is tempting because switches operate here, and it would be correct for questions about MAC-based forwarding or VLAN tagging.
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Transport layer
Why it's wrong here
The Transport layer provides end-to-end delivery, segmentation and port-based multiplexing (TCP/UDP); it never examines IP addresses to choose a path between networks. It is tempting because TCP/IP transport carries routed traffic, and it would be correct for questions about reliability, flow control or port numbers.
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Network layer
Why this is correct
The network layer handles logical addressing and path selection, forwarding packets between networks based on destination IP addresses. Data link addresses frames by MAC, transport segments by port, so routing decisions belong exclusively to layer 3.
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Physical layer
Why it's wrong here
The Physical layer transmits raw bits over the medium, defining voltages, cabling and signalling; it has no concept of IP addresses or packet headers. It is tempting because cabling faults cause connectivity loss, and it would be correct for questions about media types, pinouts or signal encoding.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official ISC2 exam blueprint
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