Question 1,909 of 2,015

EtherChannel →mediumMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the port-channel interface itself was not configured as an access port in VLAN 10, causing the EtherChannel not to form due to a VLAN mismatch. For an EtherChannel to successfully bundle, all physical member ports and the logical port-channel interface must share identical Layer 2 configurations, including the VLAN assignment on access ports. If the physical ports are set to access VLAN 10 but the port-channel interface remains in its default state (often VLAN 1 or a trunk), the switch sees a mismatch and prevents the channel from coming up. On the ENCOR 350-401 exam, this scenario tests your understanding that the port-channel interface inherits no configuration from the physical ports—you must explicitly configure it. A common trap is assuming the physical port settings automatically propagate to the logical interface. Remember the memory tip: “Match the port-channel to the ports—same VLAN, same type, or the bundle won’t ignite.”

350-401 EtherChannel Practice Question

This 350-401 practice question tests your understanding of etherchannel. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. 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.

A network engineer is configuring EtherChannel between two Cisco Catalyst switches. The ports are configured as access ports in VLAN 10. After configuring the port-channel interface and adding the physical ports, the engineer notices that the EtherChannel does not come up. The show etherchannel summary command shows the port-channel in a down state. 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.

Question 1mediummultiple choice

Open the full VLAN trunking answer →

A
The physical ports are configured as access ports in VLAN 10, but the port-channel interface is not configured with the same VLAN.
Correct because the port-channel interface must have the same access VLAN as the physical ports, or the channel will not form.
B
The physical ports have different duplex settings.
Why wrong: Incorrect because duplex mismatch would cause issues, but the scenario states the ports are configured identically as access ports, so duplex should match.
C
The switch is using PAgP and the neighbor is using LACP.
Why wrong: Incorrect because if both sides use different protocols, the channel will not form, but the scenario does not specify protocol mismatch.
D
The physical ports are in different VLANs.
Why wrong: Incorrect because the scenario says both are in VLAN 10, so VLANs match.

Full breakdown with real-world context →

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 physical ports are configured as access ports in VLAN 10, but the port-channel interface is not configured with the same VLAN.

The correct answer is that the physical ports must be configured identically, including the allowed VLAN list. For access ports, the VLAN must match. The wrong answers involve issues that would not prevent the channel from forming if the VLANs match.

Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.

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 physical ports are configured as access ports in VLAN 10, but the port-channel interface is not configured with the same VLAN.
Why this is correct
Correct because the port-channel interface must have the same access VLAN as the physical ports, or the channel will not form.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
✗
The physical ports have different duplex settings.
Why it's wrong here
Incorrect because duplex mismatch would cause issues, but the scenario states the ports are configured identically as access ports, so duplex should match.
✗
The switch is using PAgP and the neighbor is using LACP.
Why it's wrong here
Incorrect because if both sides use different protocols, the channel will not form, but the scenario does not specify protocol mismatch.
✗
The physical ports are in different VLANs.
Why it's wrong here
Incorrect because the scenario says both are in VLAN 10, so VLANs match.

Common exam traps

Common exam trap: OSPF can fail even when IP connectivity looks correct

OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.

Trap categories for this question

Scenario analysis trap
Incorrect because duplex mismatch would cause issues, but the scenario states the ports are configured identically as access ports, so duplex should match.

Detailed technical explanation

How to think about this question

OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.

KKey Concepts to Remember

OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.

TExam Day Tips

Check area mismatch first when OSPF adjacency fails.
Review passive interfaces when a network is advertised but no neighbour forms.
Use show ip ospf neighbor and show ip route clues carefully.

Key takeaway

OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.

Real-world example

How this comes up in practice

A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.

What to study next

Got this wrong? Here's your next step.

Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 350-401 OSPF questions on adjacency and route selection.

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FAQ

Questions learners often ask

What does this 350-401 question test?

EtherChannel — This question tests EtherChannel — OSPF neighbours must agree on key parameters..

What is the correct answer to this question?

The correct answer is: The physical ports are configured as access ports in VLAN 10, but the port-channel interface is not configured with the same VLAN. — The correct answer is that the physical ports must be configured identically, including the allowed VLAN list. For access ports, the VLAN must match. The wrong answers involve issues that would not prevent the channel from forming if the VLANs match.

What should I do if I get this 350-401 question wrong?

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?

OSPF neighbours must agree on key parameters.

About these practice questions

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Same concept, more angles

1 more ways this is tested on 350-401

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. A network engineer is troubleshooting an EtherChannel between two Cisco switches. The show etherchannel summary command shows the port-channel is up, but the show interfaces trunk command shows that the trunk is not passing traffic for VLAN 100. The allowed VLAN list on the port-channel interface includes VLAN 100. What is the most likely cause?

hard

✓ A.One of the physical ports in the EtherChannel has VLAN 100 removed from its allowed list.
B.The native VLAN is configured as VLAN 100 on one side.
C.The port-channel is configured with 'switchport trunk allowed vlan add 100' but the physical ports have 'switchport trunk allowed vlan except 100'.
D.The VLAN 100 does not exist on the switch.

Why A: The correct answer is that the VLAN is not allowed on one of the physical ports. The wrong answers involve issues that would affect all VLANs or are unrelated.

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