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.
In a DMVPN network with VRF-Lite, Router R1 (hub) and R2 (spoke) are configured for VRF-A. The DMVPN tunnel is up, but spoke-to-spoke traffic between R2 and R3 (another spoke) fails. R1 has configuration: interface Tunnel0, ip vrf forwarding VRF-A, ip address 172.16.0.1 255.255.255.0, tunnel source Gig0/0, tunnel mode gre multipoint. R2 has similar configuration with tunnel destination dynamic. The NHRP map for R3 is missing on R2. 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 NHRP mapping for R3 is missing on R2, preventing direct spoke-to-spoke tunnel establishment.
In DMVPN, spoke-to-spoke tunnels require NHRP resolution. If R2 does not have an NHRP map for R3, it cannot establish a direct tunnel. The hub (R1) should facilitate NHRP resolution, but if the VRF configuration is not properly propagated, NHRP may fail. The root cause is that the NHRP mapping is missing, often due to VRF mismatch in NHRP configuration or because the hub is not properly forwarding NHRP requests.
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 NHRP mapping for R3 is missing on R2, preventing direct spoke-to-spoke tunnel establishment.
Why this is correct
Correct: Without NHRP mapping, R2 cannot send traffic directly to R3; it must go through the hub.
Related concept
Static NAT maps one inside address to one outside address.
✗
The tunnel mode should be gre multipoint on all spokes.
Why it's wrong here
Incorrect: Spokes typically use tunnel mode gre multipoint or point-to-point; the issue is NHRP.
✗
The VRF must be removed from the tunnel interface for DMVPN to work.
Why it's wrong here
Incorrect: VRF can be used with DMVPN; the issue is NHRP.
✗
The hub router must have a static route for each spoke.
Why it's wrong here
Incorrect: DMVPN uses dynamic routing; static routes are not required.
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 NHRP mapping for R3 is missing on R2, preventing direct spoke-to-spoke tunnel establishment. — In DMVPN, spoke-to-spoke tunnels require NHRP resolution. If R2 does not have an NHRP map for R3, it cannot establish a direct tunnel. The hub (R1) should facilitate NHRP resolution, but if the VRF configuration is not properly propagated, NHRP may fail. The root cause is that the NHRP mapping is missing, often due to VRF mismatch in NHRP configuration or because the hub is not properly forwarding NHRP requests.
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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