- 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.
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."
JNCIA-JUNOS Routing Fundamentals Practice Question
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.
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.
Option B is correct because BGP route reflection only sends routes that are valid (i.e., routable). The 'non-routable' flag indicates that the next-hop is not reachable via the IGP (or any route) in the route reflector's routing table. Even if the next-hop is reachable from the client, the route reflector must have a route to the next-hop to advertise the prefix to clients. Option A is incorrect; cluster-id is used to detect loops, not to suppress routes. Option C is incorrect; the ORIGINATOR_ID attribute is set by the route reflector, but it does not suppress the route. Option D is incorrect; the route reflector does not modify the next-hop by default; the client must have a route to the next-hop.
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 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 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: 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.
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Routing Fundamentals — study guide chapter
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FAQ
Questions learners often ask
What does this JNCIA-JUNOS question test?
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 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. — Option B is correct because BGP route reflection only sends routes that are valid (i.e., routable). The 'non-routable' flag indicates that the next-hop is not reachable via the IGP (or any route) in the route reflector's routing table. Even if the next-hop is reachable from the client, the route reflector must have a route to the next-hop to advertise the prefix to clients. Option A is incorrect; cluster-id is used to detect loops, not to suppress routes. Option C is incorrect; the ORIGINATOR_ID attribute is set by the route reflector, but it does not suppress the route. Option D is incorrect; the route reflector does not modify the next-hop by default; the client must have a route to the next-hop.
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.
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Last reviewed: Jun 24, 2026
This JNCIA-JUNOS practice question is part of Courseiva's free Juniper Networks certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the JNCIA-JUNOS exam.
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