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200-901 Practice Question: Deploying a new data center network using Cisco…
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?
⚠ Common exam trap
Cisco often tests the subtle limitation of the peer-gateway feature: it does not respond to ARP requests received over the vPC peer-link, which candidates may overlook if they assume peer-gateway makes both switches respond identically to all ARP requests for the virtual IP.
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 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.
With active/standby NIC teaming, the server sends ARP requests for the default gateway from the active NIC. If the active NIC is connected to NX2 (the standby vPC peer for that server's MAC), NX2 receives the ARP request and forwards it over the peer-link to NX1. The peer-gateway feature allows a vPC peer to respond to ARP requests for the virtual gateway IP, but it does not respond to ARP requests received over the peer-link (only to those received on a vPC member port). Therefore, NX1 does not respond, and the ARP request times out, causing intermittent connectivity.
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.
Quick reference
Access Control Model Comparison
| Model | Acronym | Who Controls Access? | Best For |
|---|---|---|---|
| Discretionary Access Control | DAC | Resource owner | Small teams, file shares |
| Mandatory Access Control | MAC | System / security labels | Classified govt / military |
| Role-Based Access Control | RBAC | Administrator (via roles) | Enterprise environments |
| Attribute-Based Access Control | ABAC | Policy engine (user + resource attributes) | Fine-grained, dynamic policies |
| Rule-Based Access Control | RuBAC | System rules / ACLs | Firewall rules, network ACLs |
Go deeper
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.