The answer is an OSPFv3 area mismatch on the interfaces. Even when two directly connected routers have full IPv6 link-local connectivity and can ping each other, OSPFv3 adjacency will fail if their interfaces belong to different areas because the protocol requires area ID agreement as a fundamental neighbor parameter. This is a common trap on the CCNA 200-301 v2 exam: candidates often assume that successful link-local ping guarantees OSPFv3 adjacency, but the exam tests that OSPFv3 still enforces strict protocol alignment—area, network type, and authentication—just like its IPv4 counterpart. The key takeaway is that IPv6 reachability is necessary but not sufficient for OSPFv3 neighbor formation; the area must match on the shared link. Memory tip: “Ping proves the path, but area proves the pact.”
CCNA IP Routing Practice Question
This 200-301 practice question tests your understanding of ip routing. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: oSPFv3 requires all routers on a common link to be configured in the same OSPF area to successfully form neighbor adjacencies.. 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 directly connected routers running OSPFv3 do not form an adjacency. Both interfaces have valid IPv6 addresses and can ping each other using link-local addresses. 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.
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.
The most likely cause is an OSPFv3 area mismatch on the interface. In practical terms, OSPFv3 still requires neighbors on the same link to agree on the area assignment, just as OSPF for IPv4 does. Link-local reachability alone is not enough to form an adjacency. The protocol parameters still have to match.
This is an important IPv6 routing point because people sometimes assume that successful IPv6 ping means the routing protocol should automatically work. It does not. Adjacency depends on protocol alignment, not just basic connectivity.
Key principle: OSPFv3 requires all routers on a common link to be configured in the same OSPF area to successfully form neighbor adjacencies.
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 OSPFv3 neighbors on the same link must agree on the area.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPFv3 requires all routers on a common link to be configured in the same OSPF area to successfully form neighbor adjacencies.
✗
The routers need global unicast addresses before OSPFv3 can run.
Why it's wrong here
This is wrong because OSPFv3 can form neighbor relationships using link-local communication on the link.
When this WOULD be correct
In a different scenario where the question specifies that OSPFv3 is configured to require global unicast addresses for its operation, and the routers are only configured with link-local addresses, this option would be correct as it would prevent adjacency formation.
✗
The router IDs must be identical before adjacency can form.
Why it's wrong here
This is wrong because router IDs must be unique, not identical.
When this WOULD be correct
In a different scenario, if the question specified that both routers were configured with the same router ID, and that was a requirement for forming an adjacency, then this option would be correct. For example, if the question stated that the routers were misconfigured to have the same router ID, it would prevent adjacency.
✗
The link-local addresses must be learned from DHCPv6.
Why it's wrong here
This is wrong because link-local addresses do not require DHCPv6 in this way.
When this WOULD be correct
In a different scenario where the question specifies that OSPFv3 is configured on routers that only have link-local addresses and no global unicast addresses are assigned, this option would be correct. The question could state that the routers are unable to form an OSPFv3 adjacency due to the absence of global unicast addresses, which are necessary for routing beyond the local link.
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 OSPFv3 neighbors on the same link must agree on the area.
✗The routers need global unicast addresses before OSPFv3 can run.Wrong answer — click to see why▾
Why this is wrong here
This option is incorrect because OSPFv3 can operate using link-local addresses, and global unicast addresses are not a requirement for forming OSPFv3 adjacencies. The routers can still communicate using their link-local addresses.
★ When this WOULD be the correct answer
In a different scenario where the question specifies that OSPFv3 is configured to require global unicast addresses for its operation, and the routers are only configured with link-local addresses, this option would be correct as it would prevent adjacency formation.
Why candidates choose this
Candidates may choose this option due to a common misconception that OSPF requires global unicast addresses, leading them to overlook the capabilities of OSPFv3 with link-local addresses.
✗The router IDs must be identical before adjacency can form.Wrong answer — click to see why▾
Why this is wrong here
This option is wrong because OSPFv3 does not require router IDs to be identical for adjacency to form; each router can have a unique router ID. Adjacency formation depends on other factors such as matching OSPF parameters and area configurations.
★ When this WOULD be the correct answer
In a different scenario, if the question specified that both routers were configured with the same router ID, and that was a requirement for forming an adjacency, then this option would be correct. For example, if the question stated that the routers were misconfigured to have the same router ID, it would prevent adjacency.
Why candidates choose this
Candidates might choose this option due to a misunderstanding of OSPFv3 requirements, conflating the need for unique router IDs with adjacency formation, as they may have encountered similar concepts in other routing protocols.
✗The link-local addresses must be learned from DHCPv6.Wrong answer — click to see why▾
Why this is wrong here
This option is incorrect because OSPFv3 can operate using link-local addresses without the need for global unicast addresses. The OSPFv3 protocol is designed to work with link-local addresses for neighbor discovery and adjacency formation.
★ When this WOULD be the correct answer
In a different scenario where the question specifies that OSPFv3 is configured on routers that only have link-local addresses and no global unicast addresses are assigned, this option would be correct. The question could state that the routers are unable to form an OSPFv3 adjacency due to the absence of global unicast addresses, which are necessary for routing beyond the local link.
Why candidates choose this
Candidates may choose this option due to a misunderstanding of OSPFv3 requirements, mistakenly believing that global unicast addresses are mandatory for any OSPFv3 operation, leading to confusion about the protocol's capabilities.
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
A frequent exam trap is to assume that because two routers can ping each other using IPv6 link-local addresses, their OSPFv3 adjacency should automatically form. This mistake overlooks the critical requirement that both routers must be configured in the same OSPFv3 area. Candidates might also incorrectly believe that global unicast addresses are necessary for OSPFv3 adjacency or that router IDs must be identical. These misconceptions lead to selecting incorrect answers, as adjacency depends on matching area IDs and unique router IDs, not on global addressing or identical IDs.
Detailed technical explanation
How to think about this question
OSPFv3 is the version of the OSPF routing protocol designed to support IPv6 networks. It uses IPv6 link-local addresses for neighbor discovery and adjacency formation, which means routers communicate directly over the local link without requiring global unicast addresses. The core concept is that OSPFv3 neighbors must be configured in the same OSPF area to exchange routing information and form adjacencies. This area consistency ensures that routers share a common routing domain and can synchronize their link-state databases.
The decision process for OSPFv3 adjacency formation involves several checks: routers must be directly connected, have matching area IDs on their interfaces, agree on interface types, and have compatible authentication settings if enabled. Even if routers can ping each other using link-local addresses, a mismatch in the OSPF area configuration prevents adjacency formation. This is because OSPF treats area ID as a fundamental parameter for neighbor relationships, and any discrepancy causes the routers to reject adjacency.
A common exam trap is assuming that successful IPv6 ping between routers guarantees OSPFv3 adjacency. While link-local ping confirms Layer 3 reachability, OSPFv3 adjacency depends on protocol-level parameters matching exactly. Another practical behavior is that router IDs must be unique but not identical; identical router IDs cause adjacency failure but are not a prerequisite for adjacency. Understanding these nuances helps avoid misconfiguration and troubleshooting errors in IPv6 OSPF deployments.
KKey Concepts to Remember
OSPFv3 requires all routers on a common link to be configured in the same OSPF area to successfully form neighbor adjacencies.
OSPFv3 uses IPv6 link-local addresses for neighbor discovery and adjacency formation, so global unicast addresses are not mandatory for adjacency.
Each OSPF router must have a unique router ID; identical router IDs prevent adjacency formation but are not required to be the same.
Link-local addresses in IPv6 are automatically configured and do not require DHCPv6 for OSPFv3 neighbor communication.
OSPFv3 adjacency formation depends on matching protocol parameters such as area ID, interface type, and authentication settings.
Successful IPv6 ping using link-local addresses confirms basic Layer 3 connectivity but does not guarantee OSPFv3 adjacency.
OSPFv3 adjacency failure often results from configuration mismatches rather than physical or Layer 3 connectivity issues.
OSPFv3 maintains similar adjacency rules as OSPFv2, emphasizing the importance of consistent area configuration across neighbors.
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 all routers on a common link to be configured in the same OSPF area to successfully form neighbor adjacencies.
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 all routers on a common link to be configured in the same OSPF area to successfully form neighbor adjacencies., then practise related 200-301 questions on the same topic to reinforce the concept.
IP Routing — This question tests IP Routing — OSPFv3 requires all routers on a common link to be configured in the same OSPF area to successfully form neighbor adjacencies..
What is the correct answer to this question?
The correct answer is: The interfaces are assigned to different OSPFv3 areas. — The most likely cause is an OSPFv3 area mismatch on the interface. In practical terms, OSPFv3 still requires neighbors on the same link to agree on the area assignment, just as OSPF for IPv4 does. Link-local reachability alone is not enough to form an adjacency. The protocol parameters still have to match.
This is an important IPv6 routing point because people sometimes assume that successful IPv6 ping means the routing protocol should automatically work. It does not. Adjacency depends on protocol alignment, not just basic connectivity.
What should I do if I get this 200-301 question wrong?
Review oSPFv3 requires all routers on a common link to be configured in the same OSPF area to successfully form neighbor adjacencies., 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 all routers on a common link to be configured in the same OSPF area to successfully form neighbor adjacencies.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.