This N10-009 practice question tests your understanding of network implementation. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 router receives a packet destined for 10.0.0.15. It has the following routes in the routing table: 10.0.0.0/8 via 192.168.1.1, 10.0.0.0/16 via 192.168.2.1, 0.0.0.0/0 via 192.168.3.1. Which route will be used?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
10.0.0.0/16 via 192.168.2.1
The router will use the route 10.0.0.0/16 via 192.168.2.1 because it has the longest prefix match (16 bits) for the destination 10.0.0.15. The /16 route is more specific than the /8 route and the default route, so it is preferred regardless of administrative distance or metric.
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.
✗
Default route (0.0.0.0/0)
Why it's wrong here
The default route is the least specific and only used if no other route matches.
✓
10.0.0.0/16 via 192.168.2.1
Why this is correct
This route has a longer prefix length (16) than the /8 route, and it matches the destination (10.0.0.15 is in 10.0.0.0/16).
Related concept
Read the scenario before looking for a memorised answer.
✗
10.0.0.0/8 via 192.168.1.1
Why it's wrong here
Although this route also matches, it is less specific than the /16 route, so it is not chosen.
✗
None; the packet is dropped
Why it's wrong here
There are matching routes, so the packet is not dropped.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume administrative distance or metric determines the route selection, but the longest prefix match always takes precedence over these metrics when multiple routes match the destination.
Detailed technical explanation
How to think about this question
The longest prefix match algorithm is fundamental to IP routing; the router performs a bitwise comparison of the destination address against each route's prefix and selects the route with the highest number of matching bits. In this scenario, 10.0.0.15 falls within both 10.0.0.0/8 and 10.0.0.0/16, but the /16 route matches the first 16 bits (10.0) exactly, while the /8 only matches the first 8 bits. This behavior is defined in RFC 1812 and is implemented in all IP forwarding engines, including Cisco IOS, where the 'show ip route' command displays the best route based on prefix length first.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this N10-009 question in full detail.
Network Implementation — This question tests Network Implementation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 10.0.0.0/16 via 192.168.2.1 — The router will use the route 10.0.0.0/16 via 192.168.2.1 because it has the longest prefix match (16 bits) for the destination 10.0.0.15. The /16 route is more specific than the /8 route and the default route, so it is preferred regardless of administrative distance or metric.
What should I do if I get this N10-009 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.
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Question Discussion
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