Question 383 of 500

Network →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is an LACP system priority mismatch between the vPC peers, which causes the LACP system identifier to differ and triggers the port-channel flaps. In a vPC topology, both Nexus switches must present a consistent LACP system identifier to the downstream server so it sees a single logical partner; when the system priority differs, the server detects multiple partners, generating the "partner not on same aggregator" error and causing the link to drop every 5–10 minutes. This scenario tests your understanding of vPC LACP requirements on the Cisco DCCOR 350-601 exam, where a common trap is to overlook that system priority must be explicitly matched across peers—unlike standard port-channels where each switch can have its own priority. The key memory tip is "vPC = one virtual partner, so LACP system ID must be identical across both peers."

350-601 Network Practice Question

This 350-601 practice question tests your understanding of network. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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.

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?

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.

Question 1hardmultiple choice

Full question →

A
The LACP fast rate timer default changed to slow in the new software, causing a timeout mismatch with the server.
Why wrong: LACP rate mismatch would cause constant timeout and the log message would be different.
B
The vPC delay-restore timer is set too low, causing the vPC to prematurely come up before LACP is fully up.
Why wrong: Delay-restore timer affects only initial recovery after a failure, not ongoing link flaps.
C
The vPC peer-link VLAN allowed list does not include the server's VLAN, causing intermittent drops.
Why wrong: A missing VLAN would cause persistent failure, not intermittent flaps with the specific LACP error.
D
The LACP system priority is not configured consistently between the vPC peers, causing the LACP system identifier to differ.
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.

Full breakdown with real-world context →

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.

Option C is correct because 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 D is incorrect because delay-restore timer affects recovery after link failure, not during steady-state operation.

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 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.
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 350-601 questions on switching, trunking, and access-port configuration.

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FAQ

Questions learners often ask

What does this 350-601 question test?

Network — This question tests Network — Access ports place end devices into a single VLAN..

What is the correct answer to this question?

The correct answer is: The LACP system priority is not configured consistently between the vPC peers, causing the LACP system identifier to differ. — Option C is correct because 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 D is incorrect because delay-restore timer affects recovery after link failure, not during steady-state operation.

What should I do if I get this 350-601 question wrong?

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.

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Last reviewed: Jun 24, 2026

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