This 350-401 practice question tests your understanding of etherchannel. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Nothing is missing; the configuration is valid and the EtherChannel will form with the neighbor.
The configuration uses LACP passive on both member interfaces. For LACP to negotiate, one side must be active. The neighbor is active, so that is fine. However, the port-channel interface does not have the 'switchport trunk allowed vlan' command applied; it is only on the port-channel. That is actually correct—the port-channel configuration applies to the channel. But the question asks what is missing; the answer is that the port-channel interface itself must have the allowed VLAN list, which it does. Actually, the configuration is complete. The trick is that the port-channel interface already has the allowed VLAN list. So nothing is missing. But the options might include a common mistake. Let's re-evaluate: The configuration shows the port-channel with allowed VLANs, and the member ports without. That is correct. So the answer is that nothing is missing. However, a common issue is that the member ports must also have the same allowed VLAN list if configured individually, but here they are not configured, so they inherit from the port-channel. This is fine. So the correct answer is that the configuration is valid.
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 member interfaces must also have the 'switchport trunk allowed vlan 10-20' command.
Why it's wrong here
Incorrect. Member ports inherit the allowed VLAN list from the port-channel interface.
✗
The port-channel interface must be configured with 'channel-group 1' to associate the member ports.
Why it's wrong here
Incorrect. The port-channel interface is created automatically when the member interfaces are configured with channel-group.
✓
Nothing is missing; the configuration is valid and the EtherChannel will form with the neighbor.
Why this is correct
Correct. The configuration is complete and consistent.
The member interfaces must use LACP active mode to form the channel.
Why it's wrong here
Incorrect. LACP passive works with a neighbor that is active.
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.
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.
EtherChannel — This question tests EtherChannel — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: Nothing is missing; the configuration is valid and the EtherChannel will form with the neighbor. — The configuration uses LACP passive on both member interfaces. For LACP to negotiate, one side must be active. The neighbor is active, so that is fine. However, the port-channel interface does not have the 'switchport trunk allowed vlan' command applied; it is only on the port-channel. That is actually correct—the port-channel configuration applies to the channel. But the question asks what is missing; the answer is that the port-channel interface itself must have the allowed VLAN list, which it does. Actually, the configuration is complete. The trick is that the port-channel interface already has the allowed VLAN list. So nothing is missing. But the options might include a common mistake. Let's re-evaluate: The configuration shows the port-channel with allowed VLANs, and the member ports without. That is correct. So the answer is that nothing is missing. However, a common issue is that the member ports must also have the same allowed VLAN list if configured individually, but here they are not configured, so they inherit from the port-channel. This is fine. So the correct answer is that the configuration is valid.
What should I do if I get this 350-401 question wrong?
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.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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