CCNA Switching and Network Access Practice Question
An EtherChannel uses LACP. One side is configured correctly, but the peer side has a different switchport mode on one of the member links. What is the most likely result?
⚠ Common exam trap
Do not assume LACP can resolve all configuration mismatches. Ensure all settings are consistent across member links.
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 bundle may fail to form correctly because the member-link settings are inconsistent.
The most likely result is that the bundle will not form cleanly because EtherChannel requires member links to agree on important operational settings. In practical terms, LACP negotiation alone is not enough. The links also need compatible characteristics such as switchport mode, VLAN handling, speed, and duplex where relevant. This is a common troubleshooting pattern. It tests whether you know that bundle membership depends on configuration consistency, not just on enabling LACP.
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 bundle may fail to form correctly because the member-link settings are inconsistent.
Why this is correct
When LACP is enabled on the local switch but the member links are not configured with identical parameters—such as speed, duplex, VLAN allowed lists, or trunk mode—the negotiation will fail or result in a suspended port-channel. LACP requires the same physical and administrative settings on every member link; otherwise, the misconfigured links will not join the channel group, and the bundle will either stay down or operate intermittently. The result is not a partial bundle but a failure to form the full port-channel as intended.
- ✗
The switch automatically rewrites the peer configuration to match.
Why it's wrong here
The local switch has no mechanism to modify or rewrite the configuration of a remote peer; LACP only detects and reports incompatibilities via the exchange of LACPDUs. If the remote side is configured differently, the local switch may mark the link as suspended or note a channel misconfiguration, but it cannot push a new configuration to the peer. Configuration changes must be made manually on the remote device to restore channel compatibility.
When this WOULD be correct
In a different scenario where a question asks about a switch with a feature that automatically synchronizes configurations between peers, option B could be correct. For instance, if the question described a proprietary protocol that allows automatic configuration adjustments, then this option would apply.
- ✗
LACP converts the mismatched link into a routed interface automatically.
Why it's wrong here
LACP is purely a link-aggregation control protocol; it exchanges LACPDUs to bundle physical ports into a single logical link and does not alter the Layer 3 status of an interface. A mismatched link remains a Layer 2 switchport, and it will not become a routed interface because of an EtherChannel inconsistency. To create a routed port, an administrator must explicitly enter interface configuration mode and issue the no switchport command.
When this WOULD be correct
In a different scenario where a question states that a switch is configured to automatically convert interfaces based on specific conditions, such as mismatched configurations, then this option could be correct. For instance, if the question involves a switch model that supports automatic interface type adjustments under certain circumstances.
- ✗
The mismatched link is placed in a spanning-tree blocking state.
Why it's wrong here
A mismatched EtherChannel link is not automatically shut down by spanning-tree; STP reacts to network loops and topology changes, not to LACP parameter mismatches. The inconsistent link may be placed into a suspended state by the EtherChannel driver or kept as a standalone non-aggregated link, but STP will still evaluate it based on the active spanning-tree rules. An STP blocking decision is based on bridge IDs and port costs, not on LACP configuration differences.
When this WOULD be correct
In a different scenario where the question asks about the impact of VLAN configurations on spanning tree protocol (STP) operations, this option could be correct if it stated that a VLAN mismatch could affect the root bridge election process. For example, if the question involved VLAN configurations and STP, option D could be valid.
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 bundle may fail to form correctly because the member-link settings are inconsistent.Correct answer▾
Why this is correct
When LACP is enabled on the local switch but the member links are not configured with identical parameters—such as speed, duplex, VLAN allowed lists, or trunk mode—the negotiation will fail or result in a suspended port-channel. LACP requires the same physical and administrative settings on every member link; otherwise, the misconfigured links will not join the channel group, and the bundle will either stay down or operate intermittently. The result is not a partial bundle but a failure to form the full port-channel as intended.
✗The switch automatically rewrites the peer configuration to match.Wrong answer — click to see why▾
Why this is wrong here
Switches do not automatically rewrite peer configurations; configuration changes must be made manually or via network automation tools. LACP only negotiates parameters like speed and duplex, not switchport mode or VLAN settings.
★ When this WOULD be the correct answer
In a different scenario where a question asks about a switch with a feature that automatically synchronizes configurations between peers, option B could be correct. For instance, if the question described a proprietary protocol that allows automatic configuration adjustments, then this option would apply.
Why candidates choose this
Students might think that LACP's negotiation capabilities extend to automatically correcting misconfigurations, but LACP only ensures consistent operational parameters on both ends, not switchport mode or VLAN membership.
✗LACP converts the mismatched link into a routed interface automatically.Wrong answer — click to see why▾
Why this is wrong here
LACP operates at Layer 2 and does not change the interface type; a mismatched link remains a Layer 2 interface. Converting to a routed interface requires manual configuration with 'no switchport' command.
★ When this WOULD be the correct answer
In a different scenario where a question states that a switch is configured to automatically convert interfaces based on specific conditions, such as mismatched configurations, then this option could be correct. For instance, if the question involves a switch model that supports automatic interface type adjustments under certain circumstances.
Why candidates choose this
The term 'LACP' might be confused with 'routed port' or 'Layer 3' functionality, but LACP is purely for link aggregation and does not alter the interface's Layer 2 or Layer 3 status.
✗The mismatched link is placed in a spanning-tree blocking state.Wrong answer — click to see why▾
Why this is wrong here
This is incorrect because a switchport mode mismatch in an EtherChannel typically causes the link to be suspended or placed into an errdisable state, not into a spanning-tree blocking state. Spanning tree deals with loops, not port-channel parameter mismatches.
★ When this WOULD be the correct answer
In a different scenario where the question asks about the impact of VLAN configurations on spanning tree protocol (STP) operations, this option could be correct if it stated that a VLAN mismatch could affect the root bridge election process. For example, if the question involved VLAN configurations and STP, option D could be valid.
Why candidates choose this
Students may associate VLANs and STP with EtherChannel because both involve multiple links, but the root bridge election is unrelated to EtherChannel member link consistency.
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
Interpreting Packet Capture Output for Layer 2/3 Troubleshooting
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
Switchport
A switchport is a physical or virtual interface on a network switch that connects devices like computers, printers, or other switches to a local area network.
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