CCNA Switching and Network Access Practice Question
A network engineer configures an EtherChannel between two switches. Switch A's interface is set with channel-group 1 mode active, while Switch B's identical interface is set with channel-group 1 mode auto. When verifying with show etherchannel summary, the engineer observes that the port-channel interface is down and the physical interfaces are not bundled. What is the most likely cause of the problem?
⚠ Common exam trap
Cisco often tests the confusion between LACP and PAgP mode keywords, especially the similarity between 'active' (LACP) and 'auto' (PAgP), leading candidates to assume they are compatible or to focus on priority or interface state rather than protocol mismatch.
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 mode 'auto' is a PAgP negotiation mode that is incompatible with the LACP active mode.
'active' is an LACP mode that initiates negotiations, while 'auto' is a PAgP mode that passively waits for PAgP packets. Since LACP and PAgP are incompatible protocols, the interfaces will never negotiate a bundle, leaving the port-channel down. The engineer must use matching protocol modes (e.g., both LACP active/passive or both PAgP desirable/auto) for EtherChannel to form.
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 system priority on the active side must be lower than the auto side.
Why it's wrong here
The LACP system priority is used solely to select which device makes the decision when the number of ports exceeds the maximum allowed for the bundle; it does not affect whether two interfaces can negotiate a channel. The 'auto' side is a PAgP term, and LACP system priority has no relevance when talking to a PAgP interface. No requirement exists for the active side's priority to be lower than that of a peer, and equal priorities simply fall back to the lower MAC address for tie-breaking.
- ✓
The mode 'auto' is a PAgP negotiation mode that is incompatible with the LACP active mode.
Why this is correct
The mode 'auto' is one of the two PAgP negotiation modes (the other being 'desirable'), whereas LACP uses 'active' and 'passive'. PAgP and LACP are entirely separate protocols with different frame formats and state machines, so an interface set to 'auto' cannot form an EtherChannel with an interface set to 'active'. To create a bundle with LACP, both sides must use LACP modes, such as active/active or active/passive, not PAgP modes.
- ✗
LACP requires one side to be active and the other passive; two active interfaces will not bundle.
Why it's wrong here
This statement is incorrect because LACP allows the 'active' mode to proactively send Link Aggregation Control Protocol Data Units (LACPDUs) every second, so two 'active' interfaces will discover each other and form a channel. The only LACP combination that fails is passive/passive, where neither side sends LACPDUs and both wait for the other to initiate. Thus an active/active pair is a valid and commonly used configuration, not a fault condition.
- ✗
The physical interfaces must be shut down and then re-enabled after configuring LACP for the bundle to form.
Why it's wrong here
EtherChannel negotiation begins as soon as the channel-group command is applied, because the software immediately starts sending negotiation frames on the member interfaces and processing incoming ones. Shutting down and re-enabling the physical ports is not a mandatory step; it is only a manual shortcut sometimes used in older IOS to force the ports to re-evaluate their configuration after a change. Configuration changes such as switching from PAgP to LACP take effect at the interface level without requiring a physical flap.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓The mode 'auto' is a PAgP negotiation mode that is incompatible with the LACP active mode.Correct answer▾
Why this is correct
The mode 'auto' is one of the two PAgP negotiation modes (the other being 'desirable'), whereas LACP uses 'active' and 'passive'. PAgP and LACP are entirely separate protocols with different frame formats and state machines, so an interface set to 'auto' cannot form an EtherChannel with an interface set to 'active'. To create a bundle with LACP, both sides must use LACP modes, such as active/active or active/passive, not PAgP modes.
✗The LACP system priority on the active side must be lower than the auto side.Wrong answer — click to see why▾
Why this is wrong here
LACP priority is not required for basic negotiation and does not cause a failure to bundle.
✗LACP requires one side to be active and the other passive; two active interfaces will not bundle.Wrong answer — click to see why▾
Why this is wrong here
Active/active LACP successfully negotiates, so this is not the cause.
✗The physical interfaces must be shut down and then re-enabled after configuring LACP for the bundle to form.Wrong answer — click to see why▾
Why this is wrong here
Bouncing interfaces is not required to trigger LACP negotiation.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Go deeper
Related to this question
Learn chapter
Configuring Switch Ports for Desktops, VoIP Phones, APs, IoT, and Virtualized Hosts
Key term
PAgP
Port Aggregation Protocol (PAgP) is a Cisco proprietary protocol that automatically bundles multiple physical Ethernet links into a single logical link to increase bandwidth and provide redundancy.
Key term
Link Aggregation Control Protocol
Link Aggregation Control Protocol (LACP) is a standard protocol that automatically bundles multiple physical network links into a single logical link to increase bandwidth and provide redundancy.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 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 200-301 exam.