- A
The local-preference is not applied to routes that are learned via eBGP; it only works for iBGP.
Why wrong: Local-preference is applied to both eBGP and iBGP routes.
- B
The router is not receiving the ISP-A routes for those specific prefixes; perhaps ISP-A's BGP session is missing or the prefix is not advertised.
If only ISP-B has the route, it will be active regardless of local-preference.
- C
The IGP metric to the next-hop from ISP-B is lower, causing the route to be preferred.
Why wrong: IGP metric is considered later in BGP selection, after local-preference.
- D
The MED value from ISP-A is higher than from ISP-B, overriding the local-preference.
Why wrong: MED is compared after local-preference and AS-path; it cannot override local-preference if local-preference differs.
How to Use BGP Local Preference in Junos
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.
Your company recently acquired a small office that uses a Juniper MX router to connect to two ISPs for redundancy. The router has two uplinks: xe-0/0/0 to ISP-A (next-hop 10.0.0.1) and xe-0/0/1 to ISP-B (next-hop 10.0.1.1). The router receives a full BGP table from both ISPs. You want to prefer ISP-A for most traffic, but use ISP-B as a backup. You have configured BGP with local-preference 200 on routes from ISP-A and local-preference 100 on routes from ISP-B. After committing, you check the routing table and see that for some destinations, the route from ISP-B is active despite having lower local-preference. 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.
Quick Answer
The answer is that the router is not receiving the ISP-A routes for those specific prefixes, likely because ISP-A's BGP session is down or not advertising those networks. This is correct because BGP local preference is the first tiebreaker in the best path selection algorithm on Junos; a route with local-preference 200 will always be chosen over one with 100 if both are present. If the ISP-B route is active despite its lower local-preference, it means the ISP-A route simply does not exist in the routing table for those destinations, forcing the router to use the backup. On the JNCIA-Junos exam, this scenario tests your understanding that local preference is evaluated before attributes like AS-path length or MED, and a common trap is assuming a higher local preference guarantees a route is active—it only applies if the route is actually received. Remember the memory tip: "Local preference first, but no route means no choice."
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 router is not receiving the ISP-A routes for those specific prefixes; perhaps ISP-A's BGP session is missing or the prefix is not advertised.
In BGP best path selection, local-preference is the first tie-breaker. Routes from ISP-A have local-preference 200, which is higher than ISP-B's 100, so they should be preferred. If the ISP-B route is active for some destinations, it means the ISP-A route for those prefixes is absent from the routing table. This could happen if ISP-A does not advertise those specific prefixes (e.g., due to a missing route or partial BGP table) or if the BGP session to ISP-A is down for those prefixes. Option A is incorrect because local-preference applies to both eBGP and iBGP. Option C is incorrect; IGP metric is compared after many BGP attributes, and local-preference takes precedence. Option D is incorrect because MED is only compared when routes are from the same AS, and even then, local-preference is considered first.
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 local-preference is not applied to routes that are learned via eBGP; it only works for iBGP.
Why it's wrong here
Local-preference is applied to both eBGP and iBGP routes.
- ✓
The router is not receiving the ISP-A routes for those specific prefixes; perhaps ISP-A's BGP session is missing or the prefix is not advertised.
Why this is correct
If only ISP-B has the route, it will be active regardless of local-preference.
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 IGP metric to the next-hop from ISP-B is lower, causing the route to be preferred.
- ✗
The MED value from ISP-A is higher than from ISP-B, overriding the local-preference.
Why it's wrong here
MED is compared after local-preference and AS-path; it cannot override local-preference if local-preference differs.
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 router is not receiving the ISP-A routes for those specific prefixes; perhaps ISP-A's BGP session is missing or the prefix is not advertised. — In BGP best path selection, local-preference is the first tie-breaker. Routes from ISP-A have local-preference 200, which is higher than ISP-B's 100, so they should be preferred. If the ISP-B route is active for some destinations, it means the ISP-A route for those prefixes is absent from the routing table. This could happen if ISP-A does not advertise those specific prefixes (e.g., due to a missing route or partial BGP table) or if the BGP session to ISP-A is down for those prefixes. Option A is incorrect because local-preference applies to both eBGP and iBGP. Option C is incorrect; IGP metric is compared after many BGP attributes, and local-preference takes precedence. Option D is incorrect because MED is only compared when routes are from the same AS, and even then, local-preference is considered first.
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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