The root cause is a next-hop unreachable issue in VRF BLUE, not a route-target mismatch. While the route-target import and export statements appear symmetric—VRF RED exports 100:1 and imports 100:2, while VRF BLUE exports 100:2 and imports 100:1—this configuration actually allows bidirectional route leaking, so the communities themselves are correctly matched. The asymmetry arises because VRF BLUE has a static route pointing to a next-hop that is not reachable from VRF RED, causing the return traffic to fail. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding that VRF route leaking asymmetric behavior is often due to recursive routing failures or missing VRF interfaces in the route reflector’s global table, not just the route-target values. A common trap is assuming that if one direction works, the route-target configuration must be correct; in reality, always verify next-hop reachability in both VRFs. Memory tip: “Leak both ways, but check the next-hop’s gaze.”
300-410 MPLS Operations Practice Question
This 300-410 practice question tests your understanding of mpls operations. 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.
A VRF route leaking configuration causes unexpected reachability. Router R1 has VRF RED and VRF BLUE. Configuration: 'ip vrf RED rd 100:1 route-target export 100:1 route-target import 100:2' and 'ip vrf BLUE rd 100:2 route-target export 100:2 route-target import 100:1'. Router R2 is a route reflector with 'address-family ipv4 vrf RED' and 'address-family ipv4 vrf BLUE'. A host in VRF RED can ping a host in VRF BLUE, but not vice versa. What is the root cause?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The VRF BLUE has a static route pointing to a next-hop that is not reachable from VRF RED, causing asymmetric reachability.
Route leaking via route-target import/export is asymmetric if the import and export communities are not correctly matched. In this setup, VRF RED exports 100:1 and imports 100:2, while VRF BLUE exports 100:2 and imports 100:1. This allows RED to receive routes from BLUE (import 100:2 matches export 100:2) and BLUE to receive from RED (import 100:1 matches export 100:1), so bidirectional leaking should work. However, if the route reflector is not configured to pass VPNv4 routes correctly or if there is an issue with the 'next-hop' resolution, one direction may fail. The likely cause is that the route reflector does not have the VRF interfaces in its global routing table, causing next-hop unreachable for one VRF.
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 route reflector lacks 'address-family ipv4 vrf' configuration for both VRFs, causing incomplete route propagation.
Why it's wrong here
It is configured as per scenario.
✓
The VRF BLUE has a static route pointing to a next-hop that is not reachable from VRF RED, causing asymmetric reachability.
Why this is correct
If VRF BLUE imports routes from RED but uses a static route for the return path that is not leaked, return traffic fails.
Related concept
Read the scenario before looking for a memorised answer.
✗
The route-target import/export values are reversed; they should be identical for both VRFs.
Why it's wrong here
The configuration is correct for bidirectional leaking.
✗
MPLS LDP is not enabled on the interfaces between routers, preventing label switching.
Why it's wrong here
LDP is not directly related to VRF route leaking.
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.
Trap categories for this question
Scenario analysis trap
It is configured as per scenario.
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 300-410 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Identify which 300-410 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.
MPLS Operations — This question tests MPLS Operations — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The VRF BLUE has a static route pointing to a next-hop that is not reachable from VRF RED, causing asymmetric reachability. — Route leaking via route-target import/export is asymmetric if the import and export communities are not correctly matched. In this setup, VRF RED exports 100:1 and imports 100:2, while VRF BLUE exports 100:2 and imports 100:1. This allows RED to receive routes from BLUE (import 100:2 matches export 100:2) and BLUE to receive from RED (import 100:1 matches export 100:1), so bidirectional leaking should work. However, if the route reflector is not configured to pass VPNv4 routes correctly or if there is an issue with the 'next-hop' resolution, one direction may fail. The likely cause is that the route reflector does not have the VRF interfaces in its global routing table, causing next-hop unreachable for one VRF.
What should I do if I get this 300-410 question wrong?
Identify which 300-410 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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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