- A
The next-hop for the missing prefixes is not reachable via the IGP on the route reflector; the route reflector needs a route to the next-hop to advertise the prefix.
BGP requires the next-hop to be reachable for the route to be considered valid and eligible for advertisement.
- B
The route-reflector-cluster-id is set incorrectly, causing the route reflector to drop the route to prevent loops.
Why wrong: Cluster-id only prevents loops if the route already has that cluster-id; it does not cause 'non-routable' flag.
- C
The ORIGINATOR_ID attribute from a previous route reflector is causing the route to be suppressed.
Why wrong: ORIGINATOR_ID is used to prevent loops, but it does not cause 'non-routable'.
- D
The route reflector is using the next-hop-self option and cannot resolve its own IP as a next-hop.
Why wrong: Even with next-hop-self, the route reflector sets its own IP as next-hop, which is reachable via a local interface, so it would be routable.
Why BGP Route Reflector Needs Next-Hop Reachability
This JNCIA-JUNOS practice question tests your understanding of routing fundamentals. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
You are configuring a Juniper MX router to act as a BGP route reflector for your ISP network. The router has several iBGP peers, including clients and non-clients. You have configured the route-reflector-cluster-id and set the clients. After the configuration, you notice that some prefixes are not being reflected to a specific client router. The client has a valid BGP session to the route reflector and can see other prefixes. You check the BGP routing table on the route reflector and see that the missing prefixes are present but have the 'non-routable' flag. The route reflector's BGP table shows the prefix with a next-hop that is reachable via an IGP route. What is the most likely cause?
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.
Quick Answer
The answer is that the route reflector must have a route to the next-hop in its own routing table for a prefix to be considered valid and advertised. In BGP, a route is marked as "non-routable" when the next-hop is not reachable via the IGP or any active route on the reflector itself, even if the client has a path to that next-hop. This tests your understanding of BGP route reflection next-hop reachability, a key concept on the JNCIA-Junos exam where the route reflector acts as a forwarding decision point for route advertisement. A common trap is assuming the client’s reachability is sufficient; in reality, the reflector must resolve the next-hop locally to remove the hidden or non-routable flag. Remember the memory tip: "Reflector must see the hop to drop the non-routable stop."
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 next-hop for the missing prefixes is not reachable via the IGP on the route reflector; the route reflector needs a route to the next-hop to advertise the prefix.
The correct answer is A. The 'non-routable' flag in a BGP table indicates that the route reflector does not have a valid route to the next-hop in its routing table. Even if the client can reach the next-hop, the route reflector must have an IGP route to the next-hop in order to advertise the prefix to clients. Option B is incorrect because cluster-id prevents loops in route reflection, not suppresses routes. Option C is incorrect because ORIGINATOR_ID does not suppress routes; it is used for loop prevention with cluster-id. Option D is incorrect because the route reflector does not modify next-hop by default; the client needs its own route to the next-hop, but the reflector must also have a route to the next-hop to advertise the prefix.
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 next-hop for the missing prefixes is not reachable via the IGP on the route reflector; the route reflector needs a route to the next-hop to advertise the prefix.
Why this is correct
BGP requires the next-hop to be reachable for the route to be considered valid and eligible for advertisement.
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-reflector-cluster-id is set incorrectly, causing the route reflector to drop the route to prevent loops.
Why it's wrong here
Cluster-id only prevents loops if the route already has that cluster-id; it does not cause 'non-routable' flag.
- ✗
The ORIGINATOR_ID attribute from a previous route reflector is causing the route to be suppressed.
Why it's wrong here
ORIGINATOR_ID is used to prevent loops, but it does not cause 'non-routable'.
- ✗
The route reflector is using the next-hop-self option and cannot resolve its own IP as a next-hop.
Why it's wrong here
Even with next-hop-self, the route reflector sets its own IP as next-hop, which is reachable via a local interface, so it would be routable.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
- Use explanations to understand the rule behind the answer.
TExam Day Tips
- Underline the problem statement mentally.
- 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 JNCIA-JUNOS exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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FAQ
Questions learners often ask
What does this JNCIA-JUNOS question test?
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 next-hop for the missing prefixes is not reachable via the IGP on the route reflector; the route reflector needs a route to the next-hop to advertise the prefix. — The correct answer is A. The 'non-routable' flag in a BGP table indicates that the route reflector does not have a valid route to the next-hop in its routing table. Even if the client can reach the next-hop, the route reflector must have an IGP route to the next-hop in order to advertise the prefix to clients. Option B is incorrect because cluster-id prevents loops in route reflection, not suppresses routes. Option C is incorrect because ORIGINATOR_ID does not suppress routes; it is used for loop prevention with cluster-id. Option D is incorrect because the route reflector does not modify next-hop by default; the client needs its own route to the next-hop, but the reflector must also have a route to the next-hop to advertise the prefix.
What should I do if I get this JNCIA-JUNOS question wrong?
Identify which JNCIA-JUNOS exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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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Last reviewed: Jun 24, 2026
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