CCNA Switching and Network Access Practice Question
Exhibit
SW1# show etherchannel summary Group Port-channel Protocol Ports 1 Po1(SU) LACP Gi1/0/1(P) Gi1/0/2(s)
Two switches are bundled with LACP, but only one physical link is forwarding traffic in the port-channel. What is the most likely reason?
⚠ Common exam trap
Be careful not to confuse individual link issues with overall port-channel configuration problems. Ensure all settings match across member interfaces.
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
✓
One member interface has a trunk configuration mismatch
For an EtherChannel to form correctly, the member interfaces must match on key settings such as speed, duplex, trunking, and allowed VLAN list. A mismatch keeps one link from bundling even if LACP is enabled on both sides.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
One member interface has a trunk configuration mismatch
Why this is correct
When LACP negotiates a channel, all selected member interfaces must share identical Layer 2 properties, including encapsulation, native VLAN, and the allowed VLAN list. If one physical link's trunk parameters differ—for example, it permits a different VLAN set or uses a different native VLAN—that port is placed in a suspended or individual state and omitted from the port-channel. The mismatch is detectable with 'show etherchannel summary', where the offending link appears as 'S' or 'I' rather than bundled.
- ✗
LACP requires exactly one active and one passive side only
Why it's wrong here
This statement misreads LACP's negotiation modes. Both endpoints can be set to active, in which case each switch transmits LACPDUs on the link and they reach agreement without requiring a passive peer; active/passive is only one of several valid mode pairings. A passive port merely waits for a partner's LACPDU, but an active-active pairing is fully supported and commonly deployed to make the link come up faster.
When this WOULD be correct
This would be correct if the question stated that LACP is configured with both sides set to passive, causing the bundle to fail to form because neither side initiates negotiation. In that scenario, no links would be active, not just one.
- ✗
STP blocks all but one interface inside every EtherChannel
Why it's wrong here
Spanning Tree does not evaluate or block individual physical cables that belong to an already-formed EtherChannel; it sees the bundle as one logical bridge port and runs one spanning-tree instance over the port-channel. BPDUs are sent and received through the logical interface, so no internal member link is put into the blocking state, assuming the channel itself is not a loop. If one physical link fails, the remaining members continue forwarding inside that same logical port.
When this WOULD be correct
In a scenario where multiple physical links are bundled without EtherChannel (e.g., using STP for redundancy), STP would block all but one interface to prevent loops.
- ✗
EtherChannel cannot be used on trunk ports
Why it's wrong here
EtherChannel is indifferent to the port's Layer 2 link type and can be built on trunk interfaces just as easily as on access ports. In fact, most campus distribution and core links are trunk EtherChannels that extend multiple VLANs across the bundle, with the port-channel inheriting 'switchport mode trunk' and its associated VLAN pruning. The misconception arises because the logical port-channel, not the physical members, carries the trunk configuration.
When this WOULD be correct
A question might ask: 'Which of the following is a limitation of EtherChannel?' and list options including 'EtherChannel cannot be used on trunk ports' as a distractor. In that context, it would be incorrect, but if the question were 'Which of the following is NOT a valid EtherChannel configuration?' and the correct answer was 'EtherChannel on trunk ports', then this option would be wrong. However, for it to be correct, the question would need to explicitly state that trunk ports are not supported, which is false in real-world scenarios.
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.
✓One member interface has a trunk configuration mismatchCorrect answer▾
Why this is correct
When LACP negotiates a channel, all selected member interfaces must share identical Layer 2 properties, including encapsulation, native VLAN, and the allowed VLAN list. If one physical link's trunk parameters differ—for example, it permits a different VLAN set or uses a different native VLAN—that port is placed in a suspended or individual state and omitted from the port-channel. The mismatch is detectable with 'show etherchannel summary', where the offending link appears as 'S' or 'I' rather than bundled.
✗LACP requires exactly one active and one passive side onlyWrong answer — click to see why▾
Why this is wrong here
LACP supports active-active mode where both sides are configured as active, which is a common and valid configuration. The statement that LACP requires exactly one active and one passive side is incorrect; active-passive is just one possible combination.
★ When this WOULD be the correct answer
This would be correct if the question stated that LACP is configured with both sides set to passive, causing the bundle to fail to form because neither side initiates negotiation. In that scenario, no links would be active, not just one.
Why candidates choose this
Students often confuse LACP with PAgP, which does require one side to be desirable (active) and the other to be auto (passive) in certain modes, or they may think that LACP requires a negotiation handshake with one side initiating.
✗STP blocks all but one interface inside every EtherChannelWrong answer — click to see why▾
Why this is wrong here
STP treats the entire EtherChannel as a single logical interface, so it does not block individual member links. STP will only block the port-channel itself if there is a loop, but it does not block all but one interface inside the channel.
★ When this WOULD be the correct answer
In a scenario where multiple physical links are bundled without EtherChannel (e.g., using STP for redundancy), STP would block all but one interface to prevent loops.
Why candidates choose this
Students might think that STP operates on each physical link independently within an EtherChannel, not realizing that the channel is a logical bundle. They may also confuse STP behavior with load-balancing algorithms that might not use all links equally.
✗EtherChannel cannot be used on trunk portsWrong answer — click to see why▾
Why this is wrong here
EtherChannel is commonly used on trunk ports to increase bandwidth and provide redundancy between switches. There is no restriction that prevents EtherChannel from being used on trunk ports; in fact, it is a best practice for inter-switch links.
★ When this WOULD be the correct answer
A question might ask: 'Which of the following is a limitation of EtherChannel?' and list options including 'EtherChannel cannot be used on trunk ports' as a distractor. In that context, it would be incorrect, but if the question were 'Which of the following is NOT a valid EtherChannel configuration?' and the correct answer was 'EtherChannel on trunk ports', then this option would be wrong. However, for it to be correct, the question would need to explicitly state that trunk ports are not supported, which is false in real-world scenarios.
Why candidates choose this
Students might think that trunk ports have special VLAN tagging that could interfere with EtherChannel hashing or load balancing, or they may confuse EtherChannel with access port configurations.
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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Related to this question
Learn chapter
Configuring Switch Ports for Desktops, VoIP Phones, APs, IoT, and Virtualized Hosts
Key term
EtherChannel
EtherChannel is a technology that 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
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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.