350-401 Virtualization Practice Question
A network engineer is configuring a Cisco Nexus 9000 switch as a VTEP in a VXLAN EVPN fabric. The engineer needs to specify the loopback0 interface as the source for VXLAN tunnels. Which command must be entered under the NVE interface configuration?
⚠ Common exam trap
Test-takers frequently confuse the NVE source interface command with similar commands used in other contexts, such as 'source-interface' under NTP or 'interface loopback0' to enter interface configuration.
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
✓
source-interface loopback0
The correct command to set the source interface for VXLAN tunnels on a Cisco Nexus 9000 NVE interface is 'source-interface loopback0'. This command ensures that the loopback0 IP address is used as the source IP for VXLAN encapsulated traffic, which is critical for VTEP reachability and proper tunnel establishment. Without it, the NVE interface cannot function correctly.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
vxlan source-interface loopback0
Why it's wrong here
This command is not valid in NX-OS. While it includes the correct interface, the 'vxlan' keyword is not used in this context. The NVE interface configuration mode already implies VXLAN functionality, so the correct command is simply 'source-interface loopback0'. Using this invalid command would result in a syntax error and the source would not be set.
- ✗
interface loopback0
Why it's wrong here
This command would attempt to enter the configuration mode for loopback0, but it is not valid under the NVE interface configuration. The NVE interface requires a command that specifies the source interface, not one that changes the current configuration context. Using this would result in an error or would not achieve the desired configuration.
- ✓
source-interface loopback0
Why this is correct
This command correctly sets the loopback0 interface as the source for VXLAN tunnels on the NVE interface. In Cisco NX-OS, under interface nve1, the 'source-interface loopback0' command designates the loopback interface whose IP address will be used as the source IP in the outer IP header of VXLAN encapsulated packets. This is essential for VTEP reachability and tunnel establishment.
- ✗
source loopback0
Why it's wrong here
This command is incomplete and not recognized in NX-OS under the NVE interface. The correct syntax includes the keyword 'interface' as part of the command. Omitting it would cause the device to reject the command, leaving the NVE interface without a defined source, which prevents VXLAN tunnel formation.
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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.
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.
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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.