easyMultiple Choice
350-401 Practice Question: Which LACP mode must be configured on at least…
Which LACP mode must be configured on at least one side of an EtherChannel for the channel to establish?
⚠ Common exam trap
Cisco often tests the distinction between LACP and PAgP modes, and the trap here is that candidates confuse 'Desirable' (a PAgP mode) with an LACP mode, or assume 'Passive' can initiate the negotiation.
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
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Active
LACP (Link Aggregation Control Protocol) uses two modes: Active and Passive. For an EtherChannel to form, at least one side must be configured as Active, which actively sends LACP packets to negotiate the link. If both sides are Passive, neither will initiate negotiation, and the channel will not establish.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Active
Why this is correct
Active is the correct choice because LACP Active mode proactively initiates the EtherChannel negotiation by sending LACP packets to the peer. It successfully forms a channel with a peer configured in either Active or Passive mode, making it the preferred mode for dynamic link aggregation in standards-based (IEEE 802.3ad) environments.
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Passive
Why it's wrong here
Passive is incorrect in this context because it represents the non-initiating side of LACP negotiation. A port in Passive mode only waits for and responds to incoming LACP packets; it never sends its own initiation frames. Consequently, if both ends are set to Passive, the EtherChannel will never form, so it cannot satisfy the requirement to actively negotiate the link.
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Desirable
Why it's wrong here
Desirable is not a valid LACP mode; rather, it belongs to Cisco's proprietary PAgP (Port Aggregation Protocol). While PAgP Desirable does actively initiate negotiation, it uses a different protocol and frame format than LACP. Since the question specifically targets LACP behavior, choosing Desirable indicates a confusion between PAgP's 'desirable/auto' and LACP's 'active/passive' mode naming schemes.
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On
Why it's wrong here
On is incorrect because it denotes a static EtherChannel configuration that bypasses any negotiation protocol, neither LACP nor PAgP. Placing a port in On mode forcefully bundles it into a channel without exchanging control frames, which can lead to bridging loops if the peer is not similarly configured. Since the scenario requires LACP-based negotiation, On fails because it does not initiate (or participate in) LACP signaling.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-401 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 350-401 exam.