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300-410 Practice Question: Is troubleshooting a VRF-Lite deployment where…
A network engineer is troubleshooting a VRF-Lite deployment where two routers are connected via a trunk link. Each router has two VRFs (VRF_A and VRF_B). The engineer configures subinterfaces on the trunk link, assigning each subinterface to a different VRF. However, traffic between the two routers for VRF_A is not working. The 'show vrf' command shows the VRFs are active. What is the most likely issue?
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 subinterface on Router1 is configured with 'encapsulation dot1q 10', but the subinterface on Router2 is configured with 'encapsulation dot1q 20'.
In VRF-Lite with trunk links, subinterfaces must be associated with the correct VRF and VLAN. A common mistake is not matching the VLAN IDs on the subinterfaces of both routers, or missing the 'encapsulation dot1q' command.
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 subinterface on Router1 is configured with 'encapsulation dot1q 10', but the subinterface on Router2 is configured with 'encapsulation dot1q 20'.
Why this is correct
Mismatched VLAN IDs prevent the Layer 2 frames from being correctly tagged and forwarded between the VRFs.
- ✗
The 'ip vrf forwarding VRF_A' command is missing on the main interface.
Why it's wrong here
VRF forwarding is applied on subinterfaces, not the main interface, for trunk links.
- ✗
The 'no ip routing' command is configured globally.
Why it's wrong here
Disabling IP routing would affect all traffic, not just VRF_A.
- ✗
The 'mtu' command is set differently on the two subinterfaces.
Why it's wrong here
MTU mismatch could cause packet drops, but it is less likely than a VLAN mismatch for complete traffic failure.
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Learn chapter
Introduction to ENARSI Exam and Network Fundamentals
Key term
MPLS Layer 3 VPN
A technology that uses Multiprotocol Label Switching to create secure, scalable virtual private networks that connect multiple sites at the network layer, where the service provider manages routing between customer sites.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.