Question 138 of 984
350-601 Network Practice Question
During a maintenance window, a network engineer plans to upgrade the NX-OS software on a pair of Nexus 9000 switches configured as vPC peers. The engineer wants to minimize traffic disruption. Which upgrade sequence is recommended?
⚠ Common exam trap
Cisco often tests the misconception that upgrading the primary first is safer because it is the 'leader,' but the correct sequence is to upgrade the secondary first to avoid a disruptive role transition.
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
✓
Upgrade the secondary vPC peer first, then the primary
In a vPC pair, the secondary peer is upgraded first to preserve the primary's role as the forwarding anchor. Upgrading the secondary peer allows it to reboot and rejoin the vPC domain without disrupting the data plane because the primary peer continues to forward traffic. Once the secondary is stable, the primary is upgraded, ensuring minimal traffic loss.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Upgrade both switches simultaneously using ISSU
Why it's wrong here
Issuing ISSU on both at the same time can cause vPC inconsistencies and potential traffic loss; it is not recommended.
- ✗
Reload both switches to a previous version, then upgrade
Why it's wrong here
Reloading to a previous version adds unnecessary disruption; the goal is to upgrade with minimal impact.
- ✗
Upgrade the primary vPC peer first, then the secondary
Why it's wrong here
Upgrading primary first can cause role instability; best practice is to upgrade secondary first.
- ✓
Upgrade the secondary vPC peer first, then the primary
Why this is correct
Upgrading secondary first ensures the primary remains operational; after secondary upgrade, it can take over if needed during primary upgrade.
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Last reviewed: Jun 11, 2026
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