ISC2 CC Network Security Practice Question
Which OSI layer is responsible for routing packets based on IP addresses?
⚠ Common exam trap
The trap is confusing Layer 2 MAC-based switching with Layer 3 IP-based routing; the mention of IP addresses specifically points to Layer 3.
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
✓
Layer 3 – Network
Layer 3, the Network layer, is responsible for logical addressing and routing packets based on IP addresses. It determines the best path across interconnected networks using routing protocols and forwarding tables.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Layer 3 – Network
Why this is correct
Layer 3, the network layer, handles logical addressing and path selection, forwarding packets between networks according to IP addresses. This satisfies the stem's requirement by naming the layer whose protocol data unit is the packet and whose function is routing.
- ✗
Layer 1 – Physical
Why it's wrong here
Layer 1 transmits raw bits over the physical medium and has no addressing or forwarding logic, so it cannot inspect IP addresses. Physical is tempting because cabling and signalling underpin all routing, and would be correct if the question asked which layer defines voltages, pin layouts or transmission media.
- ✗
Layer 4 – Transport
Why it's wrong here
Layer 4 segments data and manages end-to-end connections using port numbers, not IP addresses, so it cannot route packets between networks. Transport is tempting because TCP and UDP carry the traffic being routed, and would be correct if the question asked which layer provides reliable delivery or port multiplexing.
- ✗
Layer 2 – Data Link
Why it's wrong here
Layer 2 forwards frames using MAC addresses within a single broadcast domain; IP-based routing between networks happens at Layer 3, where routers read the destination IP header. Data Link is tempting because it handles local delivery and switching, which would be the answer if the question asked about MAC-address forwarding.
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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
This CC practice question is part of Courseiva's free ISC2 certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CC exam.