350-401 Infrastructure Practice Question
An engineer configures a VXLAN tunnel between two Nexus switches acting as VTEPs. The underlay is a routed Layer 3 network using OSPF, and the loopback interfaces of the VTEPs are reachable. However, hosts in the same VXLAN VNI on different VTEPs cannot communicate. Which action should the engineer take to resolve the issue?
⚠ Common exam trap
The trap here is assuming the underlay routing is at fault when the loopbacks are already reachable, leading to unnecessary OSPF or PIM changes instead of checking the NVE interface and VNI mapping.
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
✓
Configure the NVE interface with the correct source-interface and ensure the VNI is mapped to the VLAN.
The NVE interface on a Cisco Nexus VTEP must have a source-interface configured, usually a loopback, and each VNI must be mapped to a VLAN. Without these, VXLAN encapsulation and decapsulation fail, so hosts in the same VNI on different VTEPs cannot communicate. The underlay is already operational, so the fix is to correct the NVE and VNI configuration.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Configure static VXLAN tunnels between the VTEPs using the destination-udp-port command.
Why it's wrong here
Static VXLAN tunnels are not a standard configuration on Cisco Nexus switches; VXLAN typically uses a control plane such as BGP EVPN or flood-and-learn with multicast. The destination-udp-port command does not create static tunnels. This option is incorrect because it misrepresents VXLAN tunnel establishment and does not resolve the lack of communication between hosts.
- ✗
Enable OSPF on the loopback interfaces and advertise them into the underlay.
Why it's wrong here
The loopback interfaces are already reachable per the scenario, so enabling OSPF and advertising them would not address the actual fault. The underlay routing is functioning; the problem lies in the VXLAN data plane or control plane, such as missing NVE interface configuration or incorrect VNI-to-VLAN mapping. This action is redundant and does not resolve the inability of hosts to communicate across VTEPs.
- ✗
Enable PIM sparse mode on the underlay and configure a rendezvous point for multicast replication.
Why it's wrong here
PIM sparse mode is used for multicast replication in VXLAN flood-and-learn mode, but the scenario does not specify that multicast is required or that it is missing. The primary issue is likely a basic NVE or VNI configuration error. Adding PIM would not fix a missing source-interface or VNI mapping, and it introduces unnecessary complexity without addressing the root cause.
- ✓
Configure the NVE interface with the correct source-interface and ensure the VNI is mapped to the VLAN.
Why this is correct
The NVE interface must be configured with a source-interface (typically a loopback) and the VNI must be associated with the correct VLAN. Without this mapping, VXLAN encapsulation or decapsulation fails, preventing communication between hosts on different VTEPs. This is a common misconfiguration that directly causes the described symptom, making this the correct action to resolve the issue.
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.
Go deeper
Related to this question
Learn chapter
EIGRP: Basics and Advanced Configuration
Key term
Fabric Fundamentals
Fabric Fundamentals is the set of core concepts behind a network fabric, where switches and routers form a single logical system that simplifies traffic forwarding and automation.
Key term
Cisco Virtual Topology System
Cisco Virtual Topology System is a software-defined networking solution that creates and manages virtual network overlays across physical and virtual infrastructure for enterprise networks.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
This 350-401 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 350-401 exam.