The answer is an OSPFv3 area mismatch, because OSPFv3 requires both ends of a directly connected link to belong to the same area for neighbor discovery and adjacency formation. Even when link-local IPv6 addresses are correctly configured and the interfaces are up, the routers will not exchange Hello packets as valid neighbors if the area ID on one interface differs from the other; this is a fundamental protocol check that prevents routing loops and ensures a consistent topology database. On the CCNA 200-301 v2 exam, this question tests your understanding that OSPFv3 neighbor requirements mirror OSPFv2—area consistency is non-negotiable, and common traps include assuming link-local reachability alone guarantees adjacency or confusing area mismatch with network type mismatches. A quick memory tip: “Same area, same story; different area, no glory.”
CCNA IP Routing Practice Question
This 200-301 practice question tests your understanding of ip routing. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: oSPFv3 requires that both routers assign their interfaces to the same OSPF area to successfully form an adjacency over IPv6.. 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.
Two routers are directly connected over IPv6 and should form an OSPFv3 adjacency, but they do not. Link-local addressing is present on both interfaces. Which issue is most likely to prevent the adjacency?
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.
The interfaces are assigned to different OSPFv3 areas.
This is correct because OSPF neighbors on the same segment must agree on the area for adjacency formation.
B
The routers need matching hostnames before OSPFv3 can start.
Why wrong: This is wrong because hostnames do not determine OSPFv3 adjacency formation.
C
IPv6 requires a /64 only for routing protocols to function.
Why wrong: This is wrong because the specific adjacency issue here is best explained by a protocol mismatch, not a blanket statement about all IPv6 routing.
D
OSPFv3 cannot run on directly connected interfaces.
Why wrong: This is wrong because OSPFv3 is designed to run on directly connected interfaces.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The interfaces are assigned to different OSPFv3 areas.
An area mismatch is a strong and direct explanation. In plain language, even though the routers can have valid IPv6 addressing and proper link-local communication on the interface, OSPFv3 still requires the two ends of the shared segment to agree on the area context for the adjacency. If one side places the interface in one area and the other side places it in another, the routers will not treat each other as valid neighbors.
This is very similar in principle to OSPF for IPv4. Link-local addressing matters in OSPFv3, but the protocol still enforces key neighbor-formation checks. The correct answer is the one that focuses on a required protocol match rather than on a vague issue like hostname or cable color.
Key principle: OSPFv3 requires that both routers assign their interfaces to the same OSPF area to successfully form an adjacency over IPv6.
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 interfaces are assigned to different OSPFv3 areas.
Why this is correct
This is correct because OSPF neighbors on the same segment must agree on the area for adjacency formation.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPFv3 requires that both routers assign their interfaces to the same OSPF area to successfully form an adjacency over IPv6.
✗
The routers need matching hostnames before OSPFv3 can start.
Why it's wrong here
This is wrong because hostnames do not determine OSPFv3 adjacency formation.
When this WOULD be correct
In a different scenario, if the question specified that OSPFv3 requires routers to have matching hostnames for a specific proprietary implementation or feature, then this option could be correct. For example, if the exam asked about a vendor-specific OSPFv3 implementation that enforces hostname matching for security reasons.
✗
IPv6 requires a /64 only for routing protocols to function.
Why it's wrong here
This is wrong because the specific adjacency issue here is best explained by a protocol mismatch, not a blanket statement about all IPv6 routing.
When this WOULD be correct
In a different exam scenario, if the question stated that OSPFv3 was configured on a link with a prefix length other than /64 and asked whether this would affect OSPFv3 operation, then this option could be correct, as it would imply a misunderstanding of the requirements for OSPFv3.
✗
OSPFv3 cannot run on directly connected interfaces.
Why it's wrong here
This is wrong because OSPFv3 is designed to run on directly connected interfaces.
When this WOULD be correct
In a different scenario where the question states that OSPFv3 is being configured on a non-directly connected interface, such as a point-to-point link that requires additional encapsulation, this option could be correct if the exam asks about the limitations of OSPFv3 in that context.
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 interfaces are assigned to different OSPFv3 areas.Correct answer▾
Why this is correct
This is correct because OSPF neighbors on the same segment must agree on the area for adjacency formation.
✗The routers need matching hostnames before OSPFv3 can start.Wrong answer — click to see why▾
Why this is wrong here
OSPFv3 adjacency formation does not depend on hostnames; hostnames are only used for identification in show commands and have no impact on routing protocol operation.
★ When this WOULD be the correct answer
In a different scenario, if the question specified that OSPFv3 requires routers to have matching hostnames for a specific proprietary implementation or feature, then this option could be correct. For example, if the exam asked about a vendor-specific OSPFv3 implementation that enforces hostname matching for security reasons.
Why candidates choose this
Students might confuse hostname requirements with other protocols like EIGRP that use router IDs, or mistakenly think that matching hostnames are needed for neighbor relationships.
✗IPv6 requires a /64 only for routing protocols to function.Wrong answer — click to see why▾
Why this is wrong here
OSPFv3 can use any valid IPv6 prefix length, including /64, /126, or /127, for the link between routers. The /64 requirement is for SLAAC, not for routing protocols.
★ When this WOULD be the correct answer
In a different exam scenario, if the question stated that OSPFv3 was configured on a link with a prefix length other than /64 and asked whether this would affect OSPFv3 operation, then this option could be correct, as it would imply a misunderstanding of the requirements for OSPFv3.
Why candidates choose this
The /64 prefix is commonly associated with IPv6 and often required for features like SLAAC, leading students to incorrectly assume it is mandatory for all IPv6 operations, including routing.
✗OSPFv3 cannot run on directly connected interfaces.Wrong answer — click to see why▾
Why this is wrong here
OSPFv3 is specifically designed to run on directly connected interfaces, just like OSPFv2. It forms adjacencies over directly connected links to exchange routing information.
★ When this WOULD be the correct answer
In a different scenario where the question states that OSPFv3 is being configured on a non-directly connected interface, such as a point-to-point link that requires additional encapsulation, this option could be correct if the exam asks about the limitations of OSPFv3 in that context.
Why candidates choose this
Students might confuse OSPFv3 with other protocols that require intermediate devices, or think that IPv6 routing protocols have different adjacency requirements.
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?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
Focus on OSPFv3 configuration requirements like area matching, not on distractors such as hostnames or prefix length.
Detailed technical explanation
How to think about this question
OSPFv3 is the version of OSPF designed to support IPv6 routing. It uses link-local addresses on interfaces to discover neighbors and exchange routing information. Despite this, OSPFv3 requires that both routers agree on the OSPF area assignment for the interface to establish adjacency. The area ID acts as a logical grouping that defines the scope of routing information exchange and database synchronization. Without matching areas, routers will not form neighbor relationships even if the link-local communication is functional.
The adjacency formation process in OSPFv3 involves several checks, including matching hello and dead intervals, interface types, and crucially, the area ID. When two routers are connected directly, they exchange hello packets using their link-local addresses. If the area IDs differ, each router treats the other as a non-neighbor, preventing the exchange of link-state advertisements (LSAs) and routing updates. This behavior mirrors OSPF for IPv4, emphasizing the importance of consistent area configuration across all participating routers.
A common exam trap is to focus on IPv6 addressing details like subnet size or hostname configuration, which do not affect adjacency formation. While a /64 prefix is standard for IPv6 interfaces, OSPFv3 adjacency failure is rarely caused by subnet size mismatches. Similarly, hostnames are irrelevant to OSPF neighbor relationships. The practical impact of an area mismatch is that routers remain isolated in their routing domains, leading to incomplete routing tables and potential connectivity issues. Understanding this helps network engineers troubleshoot OSPFv3 adjacency problems effectively.
KKey Concepts to Remember
OSPFv3 requires that both routers assign their interfaces to the same OSPF area to successfully form an adjacency over IPv6.
Link-local IPv6 addresses enable neighbor discovery and OSPFv3 communication but do not guarantee adjacency without matching area configuration.
OSPFv3 adjacency formation depends on matching parameters such as area ID, interface type, and hello/dead intervals between neighbors.
Assigning interfaces to different OSPFv3 areas prevents routers from recognizing each other as valid neighbors, blocking adjacency formation.
OSPFv3 uses link-local addresses for neighbor communication, but area consistency is critical for the protocol's routing database synchronization.
Hostname configuration does not influence OSPFv3 adjacency; adjacency depends on protocol parameters and interface settings.
OSPFv3 is designed to operate on directly connected interfaces, enabling dynamic neighbor discovery and adjacency formation over IPv6 links.
IPv6 subnet size (such as /64) is important for general IPv6 operation but does not directly cause OSPFv3 adjacency failures.
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
OSPFv3 requires that both routers assign their interfaces to the same OSPF area to successfully form an adjacency over IPv6.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Review oSPFv3 requires that both routers assign their interfaces to the same OSPF area to successfully form an adjacency over IPv6., then practise related 200-301 questions on the same topic to reinforce the concept.
IP Routing — This question tests IP Routing — OSPFv3 requires that both routers assign their interfaces to the same OSPF area to successfully form an adjacency over IPv6..
What is the correct answer to this question?
The correct answer is: The interfaces are assigned to different OSPFv3 areas. — An area mismatch is a strong and direct explanation. In plain language, even though the routers can have valid IPv6 addressing and proper link-local communication on the interface, OSPFv3 still requires the two ends of the shared segment to agree on the area context for the adjacency. If one side places the interface in one area and the other side places it in another, the routers will not treat each other as valid neighbors.
This is very similar in principle to OSPF for IPv4. Link-local addressing matters in OSPFv3, but the protocol still enforces key neighbor-formation checks. The correct answer is the one that focuses on a required protocol match rather than on a vague issue like hostname or cable color.
What should I do if I get this 200-301 question wrong?
Review oSPFv3 requires that both routers assign their interfaces to the same OSPF area to successfully form an adjacency over IPv6., then practise related 200-301 questions on the same topic to reinforce the concept.
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?
OSPFv3 requires that both routers assign their interfaces to the same OSPF area to successfully form an adjacency over IPv6.
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