This 200-901 practice question tests your understanding of network fundamentals. 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.
You are deploying a new data center network using Cisco Nexus switches. The design uses Virtual Port Channel (vPC) to provide redundancy and increased bandwidth to servers with dual-homed NICs. The two vPC peer switches are NX1 and NX2, and they are connected via a peer-link. The servers are configured with active/standby NIC teaming. After the deployment, you notice that some ARP requests from servers are not being responded to, leading to connectivity issues. Analysis shows that when a server sends an ARP request for its default gateway (which is a virtual IP on the vPC), only one of the peer switches responds, but the response does not reach the server intermittently. The vPC is correctly configured, and the peer-gateway feature is enabled. What is the most likely cause?
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.
The virtual gateway IP is misconfigured with HSRP, causing split-brain.
Why wrong: vPC uses a single IP on both peers; HSRP is not needed.
B
STP is blocking the vPC peer-link, preventing ARP responses.
Why wrong: vPC peer-link is always forwarding; STP is not used on vPC links.
C
The server's MAC address is not pinned to the correct vPC member port.
Why wrong: MAC pinning is for bounce learning; not relevant to ARP responses.
D
The server's NIC teaming is sending ARP requests to the standby switch, which forwards them over the peer-link, and the peer-gateway feature does not respond to ARP requests received over the peer-link.
Peer-gateway only responds to ARP on vPC member ports, not on peer-link.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The server's NIC teaming is sending ARP requests to the standby switch, which forwards them over the peer-link, and the peer-gateway feature does not respond to ARP requests received over the peer-link.
If peer-gateway is enabled, each vPC peer can respond to ARP for the virtual gateway IP. However, if the ARP request is sent via the peer-link (because the server's NIC is active on one switch but the request may be flooded), the response might be blocked by the peer-link's native VLAN mismatch or STP issues. Option A is correct: The peer-gateway feature works only for packets received on a vPC member port, not on the peer-link. So if the server's NIC teaming sends traffic to the standby switch first, that switch may receive the ARP request on a vPC member port and respond, but if the request goes over the peer-link, the peer switch may not respond or the response may be dropped. Option B is wrong because vPC does not use STP on member ports. Option C is wrong because HSRP is not used with vPC peer-gateway. Option D is wrong because the issue is not about MAC pinning.
Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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 virtual gateway IP is misconfigured with HSRP, causing split-brain.
Why it's wrong here
vPC uses a single IP on both peers; HSRP is not needed.
✗
STP is blocking the vPC peer-link, preventing ARP responses.
Why it's wrong here
vPC peer-link is always forwarding; STP is not used on vPC links.
✗
The server's MAC address is not pinned to the correct vPC member port.
Why it's wrong here
MAC pinning is for bounce learning; not relevant to ARP responses.
✓
The server's NIC teaming is sending ARP requests to the standby switch, which forwards them over the peer-link, and the peer-gateway feature does not respond to ARP requests received over the peer-link.
Why this is correct
Peer-gateway only responds to ARP on vPC member ports, not on peer-link.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Access ports place end devices into a single VLAN.
Common exam traps
Common exam trap: an active trunk can still block the VLAN you need
A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.
Detailed technical explanation
How to think about this question
VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.
KKey Concepts to Remember
Access ports place end devices into a single VLAN.
Trunk ports carry multiple VLANs between switches.
Allowed VLAN lists decide which VLANs can cross a trunk.
Native VLAN mismatch can create confusing symptoms.
TExam Day Tips
→Use show vlan brief to verify access VLANs.
→Use show interfaces trunk to verify trunk state and allowed VLANs.
→Do not treat every same-VLAN issue as a routing problem.
Key takeaway
A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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
Got this wrong? Here's your next step.
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 200-901 questions on switching, trunking, and access-port configuration.
Network Fundamentals — This question tests Network Fundamentals — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: The server's NIC teaming is sending ARP requests to the standby switch, which forwards them over the peer-link, and the peer-gateway feature does not respond to ARP requests received over the peer-link. — If peer-gateway is enabled, each vPC peer can respond to ARP for the virtual gateway IP. However, if the ARP request is sent via the peer-link (because the server's NIC is active on one switch but the request may be flooded), the response might be blocked by the peer-link's native VLAN mismatch or STP issues. Option A is correct: The peer-gateway feature works only for packets received on a vPC member port, not on the peer-link. So if the server's NIC teaming sends traffic to the standby switch first, that switch may receive the ARP request on a vPC member port and respond, but if the request goes over the peer-link, the peer switch may not respond or the response may be dropped. Option B is wrong because vPC does not use STP on member ports. Option C is wrong because HSRP is not used with vPC peer-gateway. Option D is wrong because the issue is not about MAC pinning.
What should I do if I get this 200-901 question wrong?
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 200-901 questions on switching, trunking, and access-port configuration.
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?
Access ports place end devices into a single VLAN.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This 200-901 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 200-901 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.