The answer is a misconfigured join interface where the site VLAN is not allowed, which directly prevents OTV MAC learning between sites. Even when the OTV adjacency is up and the overlay interface is correctly configured, the join interface acts as the physical transport for encapsulated traffic; if the site VLAN is pruned or excluded from this trunk, the OTV edge device cannot send or receive the inner frames needed to learn remote MAC addresses. On the Cisco DCCOR 350-601 exam, this scenario tests your understanding that OTV relies on the join interface to carry the site VLAN as a native or allowed VLAN—a common trap is assuming a working adjacency guarantees MAC learning, but the adjacency only confirms Layer 3 reachability. Remember the memory tip: “Adjacency up, MACs stuck? Check the join trunk for the site VLAN’s luck.”
350-601 Network Practice Question
This 350-601 practice question tests your understanding of network. 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.
A data center design requires Layer 2 extension between two sites using OTV. The network engineer notices that MAC addresses from Site A are not learned at Site B. OTV adjacency is up, and both sites have the same overlay interface configured. Which configuration issue is most likely the 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The site VLAN is not allowed on the OTV join interface.
D is correct because the OTV join interface must have the site VLAN allowed; if the site VLAN is not permitted on the join interface, the OTV edge device cannot send or receive encapsulated traffic for that VLAN, preventing MAC address learning between sites even though the OTV adjacency is up.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 OTV control group is misconfigured on one side.
Why it's wrong here
Control group misconfiguration would affect adjacency, not MAC learning.
✗
The spanning tree root bridge is different at each site.
Why it's wrong here
OTV encapsulates STP BPDUs; different root bridges do not prevent MAC learning.
✗
The multicast group range for the overlay does not match.
Why it's wrong here
Multicast group range is for data traffic; mismatch would cause forwarding issues but not prevent MAC learning if adjacency is up.
✓
The site VLAN is not allowed on the OTV join interface.
Why this is correct
The join interface must be a trunk that carries the site VLAN for OTV to forward traffic.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between control-plane (adjacency) and data-plane (VLAN transport) issues, and the trap here is that candidates assume a working OTV adjacency guarantees all VLANs are extended, overlooking the need to explicitly allow the site VLAN on the join interface.
Detailed technical explanation
How to think about this question
OTV uses the join interface to send encapsulated traffic over the transport network; the site VLAN must be allowed on that interface (e.g., via 'switchport trunk allowed vlan' on a physical port or subinterface) so that the OTV edge device can bridge the VLAN across the overlay. A common real-world scenario is forgetting to add the site VLAN to the trunk port connecting the OTV edge device to the core switch, causing silent failure of MAC learning while OTV adjacency remains up.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network — This question tests Network — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The site VLAN is not allowed on the OTV join interface. — D is correct because the OTV join interface must have the site VLAN allowed; if the site VLAN is not permitted on the join interface, the OTV edge device cannot send or receive encapsulated traffic for that VLAN, preventing MAC address learning between sites even though the OTV adjacency is up.
What should I do if I get this 350-601 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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?
Read the scenario before looking for a memorised answer.
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