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.”
300-410 VRF-Lite Practice Question
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?
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: 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 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
Static NAT maps one inside address to one outside address.
✗
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: 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
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 300-410 NAT questions on configuration and troubleshooting.
VRF-Lite — This question tests VRF-Lite — Static NAT maps one inside address to one outside address..
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?
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 300-410 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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