- A
The ingress replication list is missing some VTEPs.
Why wrong: If ingress replication were missing, traffic would not reach the target at all, not just ARP replies.
- B
The symmetric routing configuration is missing on the leaf switches.
Why wrong: Symmetric routing is not required for Layer 2 forwarding; the issue is MAC learning.
- C
The VPC configuration between the leaf switches and ESXi hosts is incorrect.
Why wrong: VPC is working for other VMs; the issue is specific to the new VNI.
- D
The MAC address of the target VM is not being advertised in EVPN type-2 routes because the VM's MAC is learned on a different leaf switch than expected.
If the MAC is not advertised, the source VTEP will flood ARP requests but not receive replies due to unknown unicast flooding.
Quick Answer
The answer is that the target VM’s MAC address is not being advertised in EVPN type-2 routes because it was learned on a different leaf switch than expected. In a VXLAN EVPN fabric, type-2 routes carry MAC/IP information between VTEPs via BGP; if a leaf switch fails to advertise a locally learned MAC—often due to asymmetric learning or stale entries from a VM migration—the remote VTEP cannot build the correct unicast forwarding path for ARP replies, causing the intermittent connectivity and packet loss described. On the ENCOR 350-401 exam, this scenario tests your understanding of EVPN control-plane behavior versus data-plane flooding, and a common trap is to blame underlay BGP or NVE interface status when the real issue is a missing type-2 route advertisement. Remember the key: no type-2 route, no unicast reply—flooding works for ARP requests, but replies need the MAC in the control plane.
350-401 Virtualization Practice Question
This 350-401 practice question tests your understanding of virtualization. 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.
A financial services company has deployed Cisco UCS servers with VMware vSphere 7.0 to host critical trading applications. The network uses Cisco Nexus 9000 switches in a VXLAN EVPN fabric with BGP as the underlay. The environment includes 50 ESXi hosts, each connected via two 40G interfaces to two different leaf switches in a VPC. The VMs are spread across multiple hosts and communicate over VXLAN. Recently, the operations team migrated a set of VMs from an old VLAN-based network to a new VXLAN segment (VNI 50000). After the migration, users report intermittent connectivity issues and packet loss. The engineering team captures traffic and notices that some VMs send ARP requests that are not being replied to, even though the target VM is active. Further analysis shows that the ARP requests are being flooded to all VTEPs, but the replies are not reaching the source. The team checks the underlay and finds no issues with BGP or routing. The NVE interfaces are up, and the VNI is configured. Which of the following is the most likely cause of the issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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 MAC address of the target VM is not being advertised in EVPN type-2 routes because the VM's MAC is learned on a different leaf switch than expected.
The issue is that the target VM's MAC address is not being advertised via EVPN Type-2 routes from the leaf switch where it resides. When the source VM sends an ARP request, the ingress VTEP floods it to all VTEPs in the VNI's ingress replication list, but the reply from the target VM must be unicast back. If the target's MAC is not in the EVPN control plane (e.g., because it was learned on a different leaf than expected due to asymmetric MAC learning or stale entries), the reply cannot be forwarded correctly, causing intermittent connectivity.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 ingress replication list is missing some VTEPs.
Why it's wrong here
If ingress replication were missing, traffic would not reach the target at all, not just ARP replies.
- ✗
The symmetric routing configuration is missing on the leaf switches.
Why it's wrong here
Symmetric routing is not required for Layer 2 forwarding; the issue is MAC learning.
- ✗
The VPC configuration between the leaf switches and ESXi hosts is incorrect.
Why it's wrong here
VPC is working for other VMs; the issue is specific to the new VNI.
- ✓
The MAC address of the target VM is not being advertised in EVPN type-2 routes because the VM's MAC is learned on a different leaf switch than expected.
Why this is correct
If the MAC is not advertised, the source VTEP will flood ARP requests but not receive replies due to unknown unicast flooding.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between data-plane flooding (which works) and control-plane advertisement (which fails), leading candidates to incorrectly blame replication lists or VPC issues instead of identifying the missing EVPN Type-2 route.
Detailed technical explanation
How to think about this question
In VXLAN EVPN, MAC addresses are distributed via BGP EVPN Type-2 routes (MAC/IP advertisement). When a VM moves or is newly migrated, the leaf switch must advertise the MAC to the EVPN control plane. If the advertisement is missing or the MAC is learned on a different leaf (e.g., due to asymmetric MAC learning or stale entries), the ingress VTEP will not have the correct next-hop for the target MAC, causing ARP replies to be dropped. This is a common issue in migrations where the MAC table is not properly synchronized with EVPN.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
What to study next
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FAQ
Questions learners often ask
What does this 350-401 question test?
Virtualization — This question tests Virtualization — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The MAC address of the target VM is not being advertised in EVPN type-2 routes because the VM's MAC is learned on a different leaf switch than expected. — The issue is that the target VM's MAC address is not being advertised via EVPN Type-2 routes from the leaf switch where it resides. When the source VM sends an ARP request, the ingress VTEP floods it to all VTEPs in the VNI's ingress replication list, but the reply from the target VM must be unicast back. If the target's MAC is not in the EVPN control plane (e.g., because it was learned on a different leaf than expected due to asymmetric MAC learning or stale entries), the reply cannot be forwarded correctly, causing intermittent connectivity.
What should I do if I get this 350-401 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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.
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