Question 411 of 2,152

VRF-Lite →hardMultiple ChoiceObjective-mapped

VRF-Lite Route Leaking: Next-Hop Reachability Issue

This 300-410 practice question tests your understanding of vrf-lite. 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.

Router R1 is leaking routes from VRF-A to the global table using route-map LEAK. The global table receives the routes, but traffic from the global table to destinations in VRF-A is dropped. R1 configuration: ip vrf VRF-A, rd 100:1, route-target export 100:1, route-target import 100:1. The route-map LEAK is applied to the VRF export. The global table has a default route pointing to null0. What is the root cause?

A
The leaked routes have a next-hop that is only reachable within VRF-A, not in the global routing table, causing traffic to be dropped.
Correct: When leaking, the next-hop must be reachable in the destination table; otherwise, packets are dropped.
B
The global table default route is overriding the leaked routes.
Why wrong: Incorrect: Leaked routes are more specific and should override the default.
C
The route-map should be applied to the VRF import instead of export.
Why wrong: Incorrect: Export is correct for leaking from VRF to global.
D
The VRF must have a route to the global table.
Why wrong: Incorrect: The issue is global to VRF, not VRF to global.

Full breakdown with real-world context →

Quick Answer

The root cause is that the leaked routes have a next-hop reachable only within VRF-A, not in the global routing table, which causes traffic from the global table to be dropped. When VRF-Lite route leaking exports prefixes via a route-map, the global table installs those routes but retains the original next-hop address from the VRF. If that next-hop is not reachable in the global table—because it belongs to a VRF interface or a subnet not present globally—the router cannot perform a successful recursive lookup, and the leaked routes remain in a “next-hop unreachable” state. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of how route leaking interacts with recursive routing and the importance of ensuring next-hop reachability across VRFs. A common trap is assuming that simply exporting the prefix is enough, while forgetting that the global table must have a path to the next-hop. Memory tip: “Leak the route, but check the hop—if it’s in the VRF, traffic will 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 leaked routes have a next-hop that is only reachable within VRF-A, not in the global routing table, causing traffic to be dropped.

When routes are leaked from VRF to global, the global table installs them, but the reverse path (global to VRF) requires proper routing. If the global table has a default route pointing to null0, traffic to the leaked prefixes may match the default and be discarded if the leaked routes are less specific. However, the more specific leaked routes should override the default. The issue could be that the leaked routes are not being installed due to administrative distance or that the default route is preferred. But the most common cause is that the route-map does not set the next-hop correctly, or the VRF interface is not reachable from the global table. The root cause is that the leaked routes have a next-hop that is not reachable in the global table, often because the next-hop is in the 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 leaked routes have a next-hop that is only reachable within VRF-A, not in the global routing table, causing traffic to be dropped.
Why this is correct
Correct: When leaking, the next-hop must be reachable in the destination table; otherwise, packets are dropped.
Related concept
Read the scenario before looking for a memorised answer.
✗
The global table default route is overriding the leaked routes.
Why it's wrong here
Incorrect: Leaked routes are more specific and should override the default.
✗
The route-map should be applied to the VRF import instead of export.
Why it's wrong here
Incorrect: Export is correct for leaking from VRF to global.
✗
The VRF must have a route to the global table.
Why it's wrong here
Incorrect: The issue is global to VRF, not VRF to global.

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 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.

What to study next

Got this wrong? Here's your next step.

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.

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FAQ

Questions learners often ask

What does this 300-410 question test?

VRF-Lite — This question tests VRF-Lite — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The leaked routes have a next-hop that is only reachable within VRF-A, not in the global routing table, causing traffic to be dropped. — When routes are leaked from VRF to global, the global table installs them, but the reverse path (global to VRF) requires proper routing. If the global table has a default route pointing to null0, traffic to the leaked prefixes may match the default and be discarded if the leaked routes are less specific. However, the more specific leaked routes should override the default. The issue could be that the leaked routes are not being installed due to administrative distance or that the default route is preferred. But the most common cause is that the route-map does not set the next-hop correctly, or the VRF interface is not reachable from the global table. The root cause is that the leaked routes have a next-hop that is not reachable in the global table, often because the next-hop is in the VRF.

What should I do if I get this 300-410 question wrong?

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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