200-901 Network Fundamentals Practice Question
A network engineer is troubleshooting connectivity issues and wants to verify the path that packets take from a source to a destination IP address. Which OSI layer is primarily responsible for packet forwarding and routing?
⚠ Common exam trap
Cisco often tests the distinction between Layer 2 switching (MAC-based forwarding within a LAN) and Layer 3 routing (IP-based forwarding between networks), and the trap here is that candidates confuse the Data Link layer's local forwarding with the Network layer's path determination.
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
The Network layer (Layer 3) is responsible for packet forwarding and routing, using logical IP addresses to determine the best path from source to destination. Protocols like IP (IPv4/IPv6) and routing protocols (e.g., OSPF, BGP) operate at this layer to make forwarding decisions. The traceroute command is a common tool that leverages Layer 3 TTL (Time-to-Live) fields to map the path packets take.
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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Layer 4 - Transport
Why it's wrong here
Transport layer provides end-to-end communication and segmentation.
- ✓
Layer 3 - Network
Why this is correct
Network layer is responsible for packet forwarding, routing, and logical addressing.
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Layer 1 - Physical
Why it's wrong here
Physical layer deals with bits and transmission media.
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Layer 2 - Data Link
Why it's wrong here
Data Link layer handles frames and MAC addresses within a single network segment.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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