- A
Layer 4 - Transport
Why wrong: Transport layer provides end-to-end communication and segmentation.
- B
Layer 3 - Network
Network layer is responsible for packet forwarding, routing, and logical addressing.
- C
Layer 1 - Physical
Why wrong: Physical layer deals with bits and transmission media.
- D
Layer 2 - Data Link
Why wrong: Data Link layer handles frames and MAC addresses within a single network segment.
Question 343 of 1,000
200-901 Network Fundamentals Practice Question
This 200-901 practice question tests your understanding of network fundamentals. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
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.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 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.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Layer 1 - Physical
Why it's wrong here
Physical layer deals with bits and transmission media.
- ✗
Layer 2 - Data Link
Why it's wrong here
Data Link layer handles frames and MAC addresses within a single network segment.
Common exam traps
Common exam trap: answer the scenario, not the keyword
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.
Detailed technical explanation
How to think about this question
Under the hood, Layer 3 routers examine the destination IP address in the packet header and consult a routing table (populated by static routes or dynamic protocols like OSPF) to determine the next-hop interface. A subtle behavior is that traceroute works by sending packets with incrementing TTL values; each router along the path decrements the TTL and, when it reaches zero, sends an ICMP Time Exceeded message back to the source, revealing the hop. In real-world scenarios, misconfigured routing tables or asymmetric routing can cause path verification tools to show unexpected results, making Layer 3 troubleshooting critical.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
What to study next
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FAQ
Questions learners often ask
What does this 200-901 question test?
Network Fundamentals — This question tests Network Fundamentals — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 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.
What should I do if I get this 200-901 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Last reviewed: Jul 4, 2026
This 200-901 practice question is part of Courseiva's free Cisco 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 200-901 exam.
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