The answer is an unreachable BGP next-hop. When a BGP route is marked as hidden in the Junos OS, it means the route is present in the routing table but is not considered a valid candidate for active use, and the most common technical reason is that the next-hop address specified in the BGP update is not reachable via any active route in the inet.0 table. This concept is frequently tested on the JNCIA-Junos exam, often in a multiple-choice scenario where you must distinguish between hidden routes and routes that are simply not selected as best due to attributes like local preference or AS path length. A common trap is confusing a hidden route with a route that loses a best-path tiebreaker—remember that hidden means the route is effectively dead because its next-hop is missing, not that it lost a comparison. Memory tip: "Hidden means hopless"—if the next-hop is unreachable, the route stays hidden no matter how attractive its attributes are.
JNCIA-JUNOS Routing Fundamentals Practice Question
This JNCIA-JUNOS practice question tests your understanding of routing 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
show route protocol bgp
inet.0: 15 destinations, 20 routes (14 active, 0 holddown, 1 hidden)
+ = Active Route, - = Last Active, * = Both
172.16.0.0/12 *[BGP/170] 00:01:20, MED 0, localpref 100, from 192.168.1.1
AS path: 64500 65000 I
> to 10.0.0.2 via ge-0/0/0.0
10.0.0.0/8 *[BGP/170] 00:02:00, MED 0, localpref 200, from 192.168.1.2
AS path: 64500 I
> to 10.0.0.1 via ge-0/0/0.0
192.168.0.0/16 [BGP/170] 00:01:00, MED 0, localpref 100, from 192.168.1.1
AS path: 64500 65000 I
(hidden)
Refer to the exhibit. The route for 192.168.0.0/16 is hidden. What is the most likely reason?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
show route protocol bgp
inet.0: 15 destinations, 20 routes (14 active, 0 holddown, 1 hidden)
+ = Active Route, - = Last Active, * = Both
172.16.0.0/12 *[BGP/170] 00:01:20, MED 0, localpref 100, from 192.168.1.1
AS path: 64500 65000 I
> to 10.0.0.2 via ge-0/0/0.0
10.0.0.0/8 *[BGP/170] 00:02:00, MED 0, localpref 200, from 192.168.1.2
AS path: 64500 I
> to 10.0.0.1 via ge-0/0/0.0
192.168.0.0/16 [BGP/170] 00:01:00, MED 0, localpref 100, from 192.168.1.1
AS path: 64500 65000 I
(hidden)
A
The BGP next-hop is unreachable
Hidden routes often result from an unreachable next-hop.
B
The route has a lower local preference
Why wrong: A lower localpref would cause the route not to be selected as best, but it would still be visible, not hidden.
C
The route has a longer AS path
Why wrong: A longer AS path may cause it not to be best, but the route would still be present.
D
The route has a higher MED value
Why wrong: MED is 0, same as other routes; MED does not cause hidden state.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The BGP next-hop is unreachable
A hidden BGP route typically indicates that the next-hop is unreachable. Option A is correct. Option B is incorrect because localpref affects best path selection but does not cause hidden state. Option C is incorrect because AS path length is considered but does not hide the route. Option D is incorrect because MED is 0, same as others.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
The BGP next-hop is unreachable
Why this is correct
Hidden routes often result from an unreachable next-hop.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The route has a lower local preference
Why it's wrong here
A lower localpref would cause the route not to be selected as best, but it would still be visible, not hidden.
✗
The route has a longer AS path
Why it's wrong here
A longer AS path may cause it not to be best, but the route would still be present.
✗
The route has a higher MED value
Why it's wrong here
MED is 0, same as other routes; MED does not cause hidden state.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related JNCIA-JUNOS NAT questions on configuration and troubleshooting.
Routing Fundamentals — This question tests Routing Fundamentals — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The BGP next-hop is unreachable — A hidden BGP route typically indicates that the next-hop is unreachable. Option A is correct. Option B is incorrect because localpref affects best path selection but does not cause hidden state. Option C is incorrect because AS path length is considered but does not hide the route. Option D is incorrect because MED is 0, same as others.
What should I do if I get this JNCIA-JUNOS question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related JNCIA-JUNOS NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Refer to the exhibit. Why is the route for 192.168.1.0/24 hidden?
easy
A.The route has a higher metric
B.The route has a lower preference
C.The route is not committed
✓ D.The next-hop is unreachable
Why D: The route is hidden because its next-hop is unreachable. Option B is correct. Option A is incorrect because the metric is the same as other static routes. Option C is incorrect because the route appears in the routing table. Option D is incorrect because the preference is 10, same as other routes.
Variation 2. A static route to 10.0.0.0/8 has next-hop 192.168.1.1. The route is not installed in the routing table. Which condition must be met for the route to become active?
hard
A.The static route must have a lower preference than any dynamic route to the same prefix.
B.The next-hop must have an ARP entry in the ARP table.
✓ C.The next-hop 192.168.1.1 must be reachable via an active route (e.g., a direct or OSPF route).
D.The metric of the static route must be lower than that of any other route to the same prefix.
Why C: The correct answer is C. For a static route with an indirect next-hop, the next-hop must be reachable via another active route. This is called recursive route resolution. Option A is incorrect because static routes do not depend on an ARP entry directly; they require a route to the next-hop. Option B is incorrect because preference affects selection, not installation. Option D is incorrect because metric is not used by static routes for resolution.
Last reviewed: Jun 24, 2026
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