The answer is a protocol mismatch between LACP and PAgP. Switch A’s “active” mode uses LACP, while Switch B’s “desirable” mode uses PAgP, and these two protocols cannot interoperate—EtherChannel requires both sides to run the same negotiation protocol for the bundle to form. On the CCNA 200-301 v2 exam, this scenario tests your understanding that “active” and “passive” are LACP modes, whereas “desirable” and “auto” belong to PAgP; a common trap is assuming any combination of these keywords will work, but mixing protocols always breaks the channel. Remember the memory tip: “LACP loves active/passive, PAgP prefers desirable/auto”—if the modes don’t match protocol families, the link stays down.
CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: etherChannel bundles multiple physical Ethernet links into a single logical link to increase bandwidth and provide redundancy in Cisco networks.. 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.
Exhibit
SW1:
interface range g1/0/1-2
switchport mode trunk
channel-group 5 mode active
SW2:
interface range g1/0/1-2
switchport mode trunk
channel-group 5 mode desirable
A network administrator is configuring a Layer 2 EtherChannel between two switches. Switch A uses 'channel-group 1 mode active', and Switch B uses 'channel-group 1 mode desirable'. All member interfaces are trunk ports with identical allowed VLANs. The EtherChannel fails to form. What is the most likely 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The switches are using different EtherChannel negotiation protocols.
The two switches are using different negotiation protocols: LACP (active) on one side and PAgP (desirable) on the other. EtherChannel requires both sides to use the same protocol, so this protocol mismatch prevents the bundle from forming. The other settings—trunking, VLAN configuration, and channel-group number—are correctly configured and do not cause the failure.
Key principle: EtherChannel bundles multiple physical Ethernet links into a single logical link to increase bandwidth and provide redundancy in Cisco networks.
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 switches are using different EtherChannel negotiation protocols.
Why this is correct
LACP active cannot form a channel with PAgP desirable.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
EtherChannel bundles multiple physical Ethernet links into a single logical link to increase bandwidth and provide redundancy in Cisco networks.
✗
A Layer 2 EtherChannel cannot carry trunk links.
Why it's wrong here
Layer 2 EtherChannels commonly carry trunks.
When this WOULD be correct
In a different scenario, if the question stated that the EtherChannel was configured to carry only access links and explicitly mentioned that trunking was not allowed, this option could be correct. For example, if the question asked about the limitations of EtherChannel in a specific network design that prohibits trunking, then this would apply.
✗
The channel-group number must be different on each switch.
Why it's wrong here
The group number is locally significant and does not have to differ.
When this WOULD be correct
In a different question setup where the focus is on configuring multiple EtherChannels between the same two switches, and the exam specifies that each EtherChannel must use a unique channel-group number for different link configurations, this option would be correct.
✗
The member interfaces must be in access mode before the bundle can form.
Why it's wrong here
Trunking is supported as long as settings match.
When this WOULD be correct
In a different scenario where the question specifies that the EtherChannel is intended to carry only access links and not trunk links, this option could be correct. For instance, if the question states that the configuration is strictly for access ports and the interfaces are mistakenly set to trunk mode, this option would then apply.
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 switches are using different EtherChannel negotiation protocols.Correct answer▾
Why this is correct
LACP active cannot form a channel with PAgP desirable.
✗A Layer 2 EtherChannel cannot carry trunk links.Wrong answer — click to see why▾
Why this is wrong here
This option is incorrect because a Layer 2 EtherChannel can indeed carry trunk links, allowing multiple VLANs to be transmitted over the same logical link. The issue with the EtherChannel not forming is more likely related to mismatched negotiation protocols or other configuration errors.
★ When this WOULD be the correct answer
In a different scenario, if the question stated that the EtherChannel was configured to carry only access links and explicitly mentioned that trunking was not allowed, this option could be correct. For example, if the question asked about the limitations of EtherChannel in a specific network design that prohibits trunking, then this would apply.
Why candidates choose this
Candidates may find this option tempting because they might recall that EtherChannels have specific configurations and limitations, leading them to mistakenly believe that trunk links are not supported in any context.
✗The channel-group number must be different on each switch.Wrong answer — click to see why▾
Why this is wrong here
This option is wrong because the channel-group number must be the same on both switches for an EtherChannel to form. Different numbers would prevent the aggregation of the links.
★ When this WOULD be the correct answer
In a different question setup where the focus is on configuring multiple EtherChannels between the same two switches, and the exam specifies that each EtherChannel must use a unique channel-group number for different link configurations, this option would be correct.
Why candidates choose this
Candidates may choose this option due to a misunderstanding of EtherChannel configurations, believing that unique identifiers are necessary for each switch's channel-group, rather than recognizing the requirement for consistency.
✗The member interfaces must be in access mode before the bundle can form.Wrong answer — click to see why▾
Why this is wrong here
This option is wrong because a Layer 2 EtherChannel can indeed carry trunk links, allowing multiple VLANs to be transmitted over the same link. Therefore, the inability to form the EtherChannel is not due to the mode of the member interfaces.
★ When this WOULD be the correct answer
In a different scenario where the question specifies that the EtherChannel is intended to carry only access links and not trunk links, this option could be correct. For instance, if the question states that the configuration is strictly for access ports and the interfaces are mistakenly set to trunk mode, this option would then apply.
Why candidates choose this
Candidates may choose this option due to a common misconception that EtherChannels are limited to access mode only, leading them to believe that any trunk configuration would inherently cause issues with EtherChannel formation.
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?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
Ensure both sides of an EtherChannel use the same negotiation protocol; mismatches are a common setup error.
Detailed technical explanation
How to think about this question
EtherChannel is a technology that bundles multiple physical Ethernet links into a single logical link to increase bandwidth and provide redundancy. Cisco switches support EtherChannel using two main negotiation protocols: Port Aggregation Protocol (PAgP) and Link Aggregation Control Protocol (LACP). PAgP is Cisco proprietary, while LACP is an IEEE standard (802.3ad). Both protocols negotiate the formation of the EtherChannel bundle by exchanging protocol-specific packets to ensure that the physical links have compatible configurations before bundling.
For an EtherChannel to form successfully, both ends must use the same negotiation protocol or be configured statically (on or off). If one side uses LACP and the other uses PAgP, the negotiation packets are incompatible, preventing the channel from forming. Additionally, the physical interfaces must match in speed, duplex, VLAN membership, and trunking mode. The channel-group number is locally significant and does not need to match on both sides. Trunk links are fully supported over Layer 2 EtherChannels, and interfaces do not need to be in access mode to bundle.
A common exam trap is assuming that the channel-group numbers must match on both switches or that trunking is unsupported over EtherChannel. Another frequent mistake is confusing the negotiation protocols and expecting LACP and PAgP to interoperate. In practice, mismatched protocols cause the EtherChannel to fail silently, making it critical to verify protocol consistency. Understanding these nuances helps avoid misconfigurations and ensures reliable EtherChannel deployment in Cisco networks.
KKey Concepts to Remember
EtherChannel bundles multiple physical Ethernet links into a single logical link to increase bandwidth and provide redundancy in Cisco networks.
Cisco switches use two main EtherChannel negotiation protocols: PAgP (Cisco proprietary) and LACP (IEEE standard 802.3ad).
Both ends of an EtherChannel must use the same negotiation protocol or be statically configured for the channel to form successfully.
The channel-group number is locally significant and does not need to match on both switches for EtherChannel formation.
Layer 2 EtherChannels fully support trunk links, and member interfaces do not need to be in access mode before bundling.
Mismatched EtherChannel negotiation protocols, such as one side using LACP and the other PAgP, prevent the channel from forming.
Physical interface parameters like speed, duplex, and VLAN membership must match on all member links for EtherChannel to function correctly.
Understanding the difference between LACP and PAgP negotiation protocols is essential to avoid silent EtherChannel failures in Cisco environments.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
EtherChannel bundles multiple physical Ethernet links into a single logical link to increase bandwidth and provide redundancy in Cisco networks.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Review etherChannel bundles multiple physical Ethernet links into a single logical link to increase bandwidth and provide redundancy in Cisco networks., then practise related 200-301 questions on the same topic to reinforce the concept.
Network Services and Security — This question tests Network Services and Security — EtherChannel bundles multiple physical Ethernet links into a single logical link to increase bandwidth and provide redundancy in Cisco networks..
What is the correct answer to this question?
The correct answer is: The switches are using different EtherChannel negotiation protocols. — The two switches are using different negotiation protocols: LACP (active) on one side and PAgP (desirable) on the other. EtherChannel requires both sides to use the same protocol, so this protocol mismatch prevents the bundle from forming. The other settings—trunking, VLAN configuration, and channel-group number—are correctly configured and do not cause the failure.
What should I do if I get this 200-301 question wrong?
Review etherChannel bundles multiple physical Ethernet links into a single logical link to increase bandwidth and provide redundancy in Cisco networks., then practise related 200-301 questions on the same topic to reinforce the concept.
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?
EtherChannel bundles multiple physical Ethernet links into a single logical link to increase bandwidth and provide redundancy in Cisco networks.
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