CCNA Network Services and Security Practice Question
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?
⚠ Common exam trap
Ensure both sides of an EtherChannel use the same negotiation protocol; mismatches are a common setup error.
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 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.
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
Switch A is configured for Link Aggregation Control Protocol (LACP) using `mode active`, whereas Switch B is configured for Port Aggregation Protocol (PAgP) using `mode desirable`. LACP and PAgP are distinct EtherChannel negotiation protocols. For an EtherChannel to establish using a negotiation protocol, both connected switches must utilise the identical protocol, as they are incompatible with each other. This protocol mismatch directly causes the EtherChannel to fail.
- ✗
A Layer 2 EtherChannel cannot carry trunk links.
Why it's wrong here
Layer 2 EtherChannels are fully capable of carrying trunk links, and this is a common deployment scenario between switches. The bundle can be configured as a trunk using 802.1Q tagging to carry multiple VLANs across the combined link. An EtherChannel does not restrict the port mode; it simply aggregates multiple physical links into a single logical interface. Therefore, stating that trunk links cannot be carried is incorrect.
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 channel-group number is locally significant, meaning it only identifies the bundle on the local switch and does not need to match the peer. Both switches can use the same or different numbers without affecting the EtherChannel's formation. What actually matters is consistent physical and logical parameters on the member ports, such as speed, duplex, VLAN membership, and trunk mode.
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
There is no requirement that member interfaces be in access mode for an EtherChannel to form. The ports must have matching layer 2 settings, but those settings can be either access or trunk as long as they are consistent across all members. In practice, trunk ports with the same allowed VLAN list and native VLAN can form a bundle without any issue. Access mode is not a prerequisite for the EtherChannel to establish.
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
Switch A is configured for Link Aggregation Control Protocol (LACP) using `mode active`, whereas Switch B is configured for Port Aggregation Protocol (PAgP) using `mode desirable`. LACP and PAgP are distinct EtherChannel negotiation protocols. For an EtherChannel to establish using a negotiation protocol, both connected switches must utilise the identical protocol, as they are incompatible with each other. This protocol mismatch directly causes the EtherChannel to fail.
✗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?”
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Key term
VLAN
A VLAN logically segments a physical network into isolated broadcast domains without requiring separate physical switches.
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.
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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.