- A
The route-target export on R1 (100:1) does not match the route-target import on R2 (100:2), so R2 does not import routes from R1.
Why wrong: Incorrect. Route-target mismatch prevents MP-BGP route exchange in MPLS VPNs, but VRF-lite OSPF does not use route-targets for route propagation within the VRF.
- B
The OSPF process on R1 is not configured with the 'vrf BLUE' keyword.
Why wrong: Incorrect. The 'vrf BLUE' keyword under router ospf is correctly implied; the issue is that the interface connecting the routers is not in the VRF.
- C
The link between R1 and R2 is not in the VRF, so OSPF cannot form adjacency.
Correct. The link between R1 and R2 is not part of VRF BLUE, so OSPF cannot form an adjacency in that VRF, preventing route learning.
- D
The route 10.1.1.0/24 is being filtered by a distribute-list in OSPF.
Why wrong: Incorrect. There is no indication of a distribute-list; the root cause is the missing VRF interface assignment, not filtering.
VRF-Lite Route Leaking Failure with Mismatched Route Targets
This 300-410 practice question tests your understanding of route maps and route filtering. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: vRF-Lite. 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 network engineer is troubleshooting reachability issues in a VRF-lite environment. R1 has the following configuration: ip vrf BLUE rd 100:1 route-target export 100:1 route-target import 100:1. R2 has: ip vrf BLUE rd 100:2 route-target export 100:2 route-target import 100:2. Both routers are connected via a link in the global routing table and are running OSPF in the VRF. R1 shows: 'show ip route vrf BLUE' has a route to 10.1.1.0/24 via OSPF, but R2 shows: 'show ip route vrf BLUE' does not have this route. What is the root cause?
Quick Answer
The answer is a route-target mismatch between R1 and R2, because the route-target export 100:1 on R1 does not match the route-target import 100:2 on R2, preventing R2 from importing the OSPF-learned route. In VRF-lite, route leaking between VRFs is not automatic; even when OSPF is running within a VRF, it only propagates routes within that same VRF instance. For a route to be shared across different VRFs, the export RT on the source VRF must exactly match the import RT on the destination VRF—here, 100:1 versus 100:2 breaks that link. This scenario directly tests your understanding of VRF-lite route leaking on the Cisco CCNP ENARSI 300-410 exam, where a common trap is assuming OSPF alone will leak routes between VRFs. Remember: OSPF handles intra-VRF routing, but RT values control inter-VRF import/export. Memory tip: "RTs must match to catch the leak"—if the export and import tags don't align, the route stays stuck.
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 link between R1 and R2 is not in the VRF, so OSPF cannot form adjacency.
In VRF-lite, OSPF adjacency requires the link to be in the VRF context. The configuration shows both routers have OSPF in the VRF, but the connecting link is in the global routing table, not in VRF BLUE. Therefore, OSPF cannot form an adjacency over that link, and routes learned via OSPF within the VRF on R1 are not propagated to R2. Route-target import/export is used for MP-BGP VPNv4 route distribution, not for OSPF in VRF-lite. The correct fix is to put the link in the VRF (e.g., using 'ip vrf forwarding BLUE' on the interface).
Key principle: VRF-Lite
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-target export on R1 (100:1) does not match the route-target import on R2 (100:2), so R2 does not import routes from R1.
- ✗
The OSPF process on R1 is not configured with the 'vrf BLUE' keyword.
Why it's wrong here
Incorrect. The 'vrf BLUE' keyword under router ospf is correctly implied; the issue is that the interface connecting the routers is not in the VRF.
- ✓
The link between R1 and R2 is not in the VRF, so OSPF cannot form adjacency.
Why this is correct
Correct. The link between R1 and R2 is not part of VRF BLUE, so OSPF cannot form an adjacency in that VRF, preventing route learning.
Related concept
VRF-Lite
- ✗
The route 10.1.1.0/24 is being filtered by a distribute-list in OSPF.
Why it's wrong here
Incorrect. There is no indication of a distribute-list; the root cause is the missing VRF interface assignment, not filtering.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Candidates often confuse VRF-lite with MPLS L3VPN and assume route-target mismatch prevents route exchange, but in VRF-lite, OSPF over a link in the global table cannot form an adjacency within the VRF.
Trap categories for this question
Keyword trap
Incorrect. The 'vrf BLUE' keyword under router ospf is correctly implied; the issue is that the interface connecting the routers is not in the VRF.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- VRF-Lite
- OSPF in VRF
- Route Target (RT)
TExam Day Tips
- 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
VRF-Lite
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
What to study next
Got this wrong? Here's your next step.
Review vRF-Lite, then practise related 300-410 questions on the same topic to reinforce the concept.
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Route Maps and Route Filtering — study guide chapter
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Route Maps and Route Filtering practice questions
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FAQ
Questions learners often ask
What does this 300-410 question test?
Route Maps and Route Filtering — This question tests Route Maps and Route Filtering — VRF-Lite.
What is the correct answer to this question?
The correct answer is: The link between R1 and R2 is not in the VRF, so OSPF cannot form adjacency. — In VRF-lite, OSPF adjacency requires the link to be in the VRF context. The configuration shows both routers have OSPF in the VRF, but the connecting link is in the global routing table, not in VRF BLUE. Therefore, OSPF cannot form an adjacency over that link, and routes learned via OSPF within the VRF on R1 are not propagated to R2. Route-target import/export is used for MP-BGP VPNv4 route distribution, not for OSPF in VRF-lite. The correct fix is to put the link in the VRF (e.g., using 'ip vrf forwarding BLUE' on the interface).
What should I do if I get this 300-410 question wrong?
Review vRF-Lite, then practise related 300-410 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
VRF-Lite
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Last reviewed: Jun 18, 2026
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