350-601 Network Practice Question
An organization has deployed a pair of Nexus 93180YC-EX switches as vPC peers in a data center. The switches are connected to a server with two 10GbE interfaces configured as an LACP port-channel. The vPC configuration has been verified and was working correctly for months. After a scheduled maintenance window that included upgrading the NX-OS software from version 7.0(3)I7(1) to 7.0(3)I7(5), the server begins experiencing frequent link flaps on the port-channel. The server administrator reports that every 5-10 minutes, the link goes down for about 2 seconds and then recovers. The network team checks the logs on the Nexus switches and sees repeated messages: 'LACP-3-MISCONFIG: Port-channel <channel> is misconfigured: partner not on same aggregator.' The 'show vpc brief' output shows all vPCs in the 'up' state. The 'show port-channel summary' shows the port-channel is up with both member ports in the bundle. What is the most likely root cause?
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 LACP system priority is not configured consistently between the vPC peers, causing the LACP system identifier to differ.
In a vPC setup, both peer switches must have the same LACP system identifier (derived from system priority and MAC address) so the server sees a single logical partner. If the LACP system priority is not consistent across the peers, the system identifiers will differ, causing the server to detect multiple partners, leading to the 'partner not on same aggregator' error and link flaps. Option A is incorrect because the LACP rate timer mismatch would cause constant timeout issues, not intermittent flaps with the specific log message. Option B is incorrect because VLAN mismatch would cause persistent connectivity failures, not intermittent flaps. Option C is incorrect because delay-restore timer affects recovery after link failure, not during steady-state operation.
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 LACP fast rate timer default changed to slow in the new software, causing a timeout mismatch with the server.
Why it's wrong here
LACP rate mismatch would cause constant timeout and the log message would be different.
- ✗
The vPC delay-restore timer is set too low, causing the vPC to prematurely come up before LACP is fully up.
Why it's wrong here
Delay-restore timer affects only initial recovery after a failure, not ongoing link flaps.
- ✗
The vPC peer-link VLAN allowed list does not include the server's VLAN, causing intermittent drops.
Why it's wrong here
A missing VLAN would cause persistent failure, not intermittent flaps with the specific LACP error.
- ✓
The LACP system priority is not configured consistently between the vPC peers, causing the LACP system identifier to differ.
Why this is correct
In a vPC, the LACP system identifier must be identical on both peers to appear as a single partner to the server. Inconsistent system priority leads to different identifiers, triggering the misconfiguration log and link flaps.
Visual reference
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 |
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-601 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 350-601 exam.