BGP Route Hidden: Most Likely Reason Is Unreachable Next-Hop
This JNCIA-JUNOS practice question tests your understanding of routing 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.
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.
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)
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.
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.
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
✓
The BGP next-hop is unreachable
In JUNOS, a BGP route is hidden when the next-hop address is not reachable via any active route in the routing table. The router cannot install the route into the forwarding table because it lacks a valid path to the next-hop, causing the route to be marked as hidden. This is a common issue when the next-hop is not covered by a directly connected or static route, or when the IGP route to the next-hop is missing.
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.
✓
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
Read the scenario before looking for a memorised answer.
✗
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: answer the scenario, not the keyword
The trap here is that candidates often confuse route selection attributes (like local preference, AS path, MED) with route installation conditions, assuming a less preferred attribute hides the route, when in fact only next-hop unreachability or policy-based rejection can cause a route to be hidden in JUNOS.
Detailed technical explanation
How to think about this question
When a BGP route is hidden, you can verify the issue using 'show route advertising-protocol bgp <neighbor>' and 'show route <prefix> hidden' commands. The next-hop reachability check is fundamental to BGP route installation; if the next-hop is not in the inet.0 table, the route is suppressed. This behavior is defined in RFC 4271 and is critical for loop prevention, as BGP relies on the IGP to provide reachability to the next-hop.
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 practitioner preparing for the JNCIA-JUNOS exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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.
Routing Fundamentals — This question tests Routing Fundamentals — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The BGP next-hop is unreachable — In JUNOS, a BGP route is hidden when the next-hop address is not reachable via any active route in the routing table. The router cannot install the route into the forwarding table because it lacks a valid path to the next-hop, causing the route to be marked as hidden. This is a common issue when the next-hop is not covered by a directly connected or static route, or when the IGP route to the next-hop is missing.
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.
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?
Read the scenario before looking for a memorised answer.
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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: Option D is correct because a route is hidden in the JUNOS routing table when its next-hop is unreachable. The show route command displays only active routes; if the next-hop address is not reachable via any active interface or route, the route is suppressed (hidden) and not used for forwarding. This is a fundamental behavior of JUNOS route selection and differs from Cisco IOS, which may still display such 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: For a static route to be installed in the Junos routing table, its next-hop must be reachable via an active route in the routing table. This is because Junos performs recursive next-hop resolution: it looks up the next-hop IP address (192.168.1.1) in the routing table and requires a valid, active route (e.g., a directly connected or OSPF-learned route) to that address. Without this, the static route remains hidden and is not installed.
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