CCNA Switching and Network Access Practice Question
An EtherChannel between two switches is configured for LACP. One switch shows the member interfaces as bundled, while the other shows them as individual interfaces. Which explanation is most likely if both sides are using LACP?
⚠ Common exam trap
Don't assume LACP alone ensures bundling; check all interface settings for consistency.
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 member interface settings do not match closely enough for bundling, even though both sides use LACP.
The most likely explanation is that some other interface settings do not match, even though both sides are using the same EtherChannel protocol. In practical terms, LACP alone is not enough. The candidate member interfaces also need to agree on characteristics such as speed, duplex, switchport mode, allowed VLANs where relevant, and other channel-related settings. If they do not, one side may treat the links as separate instead of bundling them. This is a common troubleshooting pattern because it tests whether you know that EtherChannel success depends on more than just the negotiation protocol name.
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 member interface settings do not match closely enough for bundling, even though both sides use LACP.
Why this is correct
LACP negotiation alone does not guarantee bundling; the member interfaces must also share identical physical and logical parameters such as speed, duplex, VLAN membership, native VLAN, and trunk mode. If any of these settings differ, the LACP control plane will detect the mismatch and keep the ports in a standalone state. Thus, even with LACP active on both ends, inconsistent interface configurations prevent the EtherChannel from forming.
- ✗
LACP always requires one side to use PAgP as a backup.
Why it's wrong here
LACP and PAgP are separate and mutually exclusive link aggregation protocols; LACP is defined by IEEE 802.3ad/802.1AX, while PAgP is a Cisco proprietary protocol. There is no requirement for LACP to have PAgP as a backup, and they cannot run simultaneously on the same port. LACP simply uses Active/Passive modes to negotiate bundles, with no involvement of PAgP.
When this WOULD be correct
In a different scenario, a question might state that a switch is configured to use LACP but has a fallback mechanism that defaults to PAgP if LACP fails. In this case, the option would be correct as it describes a situation where LACP requires PAgP as a backup protocol.
- ✗
EtherChannel cannot operate on switch trunks.
Why it's wrong here
EtherChannel fully supports trunk links; in fact, aggregating trunk ports between switches is a common design for increasing bandwidth while preserving VLAN tagging. The IEEE 802.1Q encapsulation on each member interface must be consistent, but trunking does not preclude EtherChannel operation. Therefore, the statement that EtherChannel cannot operate on switch trunks is incorrect.
When this WOULD be correct
If a question asked about the limitations of EtherChannel configurations specifically in relation to VLANs and trunking, stating that EtherChannel cannot operate on switch trunks would be correct. For example, if the question specified that both switches were configured as access ports only, this option could be valid.
- ✗
One switch must disable STP before EtherChannel can form.
Why it's wrong here
Disabling Spanning Tree Protocol is not a prerequisite for EtherChannel formation; in fact, EtherChannel interacts with STP by presenting the bundle as a single logical port, which prevents loops while allowing redundancy. STP remains operational to maintain a loop-free topology at the logical layer. Disabling STP would actually introduce a risk of broadcast storms, so it is never required or recommended.
When this WOULD be correct
In a different scenario where the question specifies that a network design mandates disabling STP to prevent loops in a specific topology, and the exam asks about prerequisites for EtherChannel formation under those conditions, this option could be correct.
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 member interface settings do not match closely enough for bundling, even though both sides use LACP.Correct answer▾
Why this is correct
LACP negotiation alone does not guarantee bundling; the member interfaces must also share identical physical and logical parameters such as speed, duplex, VLAN membership, native VLAN, and trunk mode. If any of these settings differ, the LACP control plane will detect the mismatch and keep the ports in a standalone state. Thus, even with LACP active on both ends, inconsistent interface configurations prevent the EtherChannel from forming.
✗LACP always requires one side to use PAgP as a backup.Wrong answer — click to see why▾
Why this is wrong here
This option is incorrect because LACP (Link Aggregation Control Protocol) does not require PAgP (Port Aggregation Protocol) as a backup; they are separate protocols. LACP can operate independently without needing PAgP on either side of the EtherChannel.
★ When this WOULD be the correct answer
In a different scenario, a question might state that a switch is configured to use LACP but has a fallback mechanism that defaults to PAgP if LACP fails. In this case, the option would be correct as it describes a situation where LACP requires PAgP as a backup protocol.
Why candidates choose this
Candidates may find this option tempting because they might confuse LACP with PAgP, thinking that both protocols can work together or that one is required as a fallback for the other, leading to misconceptions about their operational requirements.
✗EtherChannel cannot operate on switch trunks.Wrong answer — click to see why▾
Why this is wrong here
This option is incorrect because EtherChannel can indeed operate on switch trunks, allowing multiple VLANs to be carried over a single logical link. The issue in the question pertains to LACP configuration mismatches, not trunking capabilities.
★ When this WOULD be the correct answer
If a question asked about the limitations of EtherChannel configurations specifically in relation to VLANs and trunking, stating that EtherChannel cannot operate on switch trunks would be correct. For example, if the question specified that both switches were configured as access ports only, this option could be valid.
Why candidates choose this
Candidates may choose this option due to a common misconception that EtherChannel configurations are incompatible with trunking, leading to confusion about the requirements for successful EtherChannel setups.
✗One switch must disable STP before EtherChannel can form.Wrong answer — click to see why▾
Why this is wrong here
This option is incorrect because Spanning Tree Protocol (STP) does not need to be disabled for EtherChannel to form; EtherChannel can operate alongside STP. Disabling STP can lead to network loops and is not a requirement for EtherChannel functionality.
★ When this WOULD be the correct answer
In a different scenario where the question specifies that a network design mandates disabling STP to prevent loops in a specific topology, and the exam asks about prerequisites for EtherChannel formation under those conditions, this option could be correct.
Why candidates choose this
Candidates might choose this option due to a common misconception that STP must be disabled to allow for EtherChannel, especially if they have encountered configurations where STP issues caused problems in bundled interfaces.
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?”
Visual reference
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Key term
Allowed VLANs
Allowed VLANs are the specific VLANs whose traffic is permitted to pass over a specific trunk link between switches, acting as an access control filter for VLAN traffic on a port.
Key term
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Written by Johnson Ajibi, MSc IT Security
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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.