JNCIA-JUNOS Networking Fundamentals Practice Question
This JNCIA-JUNOS practice question tests your understanding of networking fundamentals. 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.
Exhibit
inet.0: 4 destinations, 4 routes (4 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
0.0.0.0/0 *[Static/5] 00:00:01 > to 10.0.0.1 via ge-0/0/0.0
10.0.0.0/8 *[Direct/0] 00:00:01 > via ge-0/0/0.0
10.0.0.1/32 *[Local/0] 00:00:01 Local via ge-0/0/0.0
192.168.1.0/24 *[Static/5] 00:00:01 > to 10.0.0.2 via ge-0/0/0.0
Refer to the exhibit. A packet with destination IP 192.168.1.100 arrives. Which next-hop IP will the router use?
inet.0: 4 destinations, 4 routes (4 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
0.0.0.0/0 *[Static/5] 00:00:01 > to 10.0.0.1 via ge-0/0/0.0
10.0.0.0/8 *[Direct/0] 00:00:01 > via ge-0/0/0.0
10.0.0.1/32 *[Local/0] 00:00:01 Local via ge-0/0/0.0
192.168.1.0/24 *[Static/5] 00:00:01 > to 10.0.0.2 via ge-0/0/0.0
A
10.0.0.1
Why wrong: 10.0.0.1 is the next-hop for the default route, not for 192.168.1.0/24.
B
10.0.0.0
Why wrong: 10.0.0.0 is a network address, not a next-hop.
C
10.0.0.2
The route for 192.168.1.0/24 points to 10.0.0.2.
D
Directly connected (the packet is sent directly to 192.168.1.100)
Why wrong: The destination is not in a directly connected subnet.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
10.0.0.2
The router performs a longest-prefix match lookup in its routing table for destination 192.168.1.100. The most specific matching route is 192.168.1.0/25 via next-hop 10.0.0.2, so the router forwards the packet to 10.0.0.2. Option C is correct.
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.
✗
10.0.0.1
Why it's wrong here
10.0.0.1 is the next-hop for the default route, not for 192.168.1.0/24.
✗
10.0.0.0
Why it's wrong here
10.0.0.0 is a network address, not a next-hop.
✓
10.0.0.2
Why this is correct
The route for 192.168.1.0/24 points to 10.0.0.2.
Related concept
Read the scenario before looking for a memorised answer.
✗
Directly connected (the packet is sent directly to 192.168.1.100)
Why it's wrong here
The destination is not in a directly connected subnet.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume the route with the lower metric or administrative distance wins, but in Junos (and all IP routing), the longest-prefix match is always evaluated first, regardless of metric or preference.
Detailed technical explanation
How to think about this question
The route selection process in Junos uses the longest-prefix match algorithm, comparing the destination IP against all prefixes in the routing table. The /25 prefix (192.168.1.0/25) covers addresses 192.168.1.0–192.168.1.127, which includes .100, while the /24 prefix covers a larger range. This behavior is defined by RFC 4632 and is fundamental to classless inter-domain routing (CIDR).
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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Networking Fundamentals — This question tests Networking Fundamentals — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 10.0.0.2 — The router performs a longest-prefix match lookup in its routing table for destination 192.168.1.100. The most specific matching route is 192.168.1.0/25 via next-hop 10.0.0.2, so the router forwards the packet to 10.0.0.2. Option C is correct.
What should I do if I get this JNCIA-JUNOS 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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