Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
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?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Best answer
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
Distractor review
The routers need matching hostnames before OSPFv3 can start.
This is wrong because hostnames do not determine OSPFv3 adjacency formation.
C
Distractor review
IPv6 requires a /64 only for routing protocols to function.
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
Distractor review
OSPFv3 cannot run on directly connected interfaces.
This is wrong because OSPFv3 is designed to run on directly connected interfaces.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is to assume that IPv6 addressing details such as subnet size or hostnames influence OSPFv3 adjacency formation. Candidates might incorrectly believe that mismatched IPv6 prefixes or missing hostname configuration prevent adjacency. However, OSPFv3 adjacency strictly depends on matching protocol parameters like area ID, hello/dead intervals, and interface types. Overlooking the area mismatch leads to selecting incorrect answers related to IPv6 addressing or interface configuration. Recognizing that area consistency is mandatory helps avoid this trap and correctly diagnose adjacency issues.
Technical deep dive
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.
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More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?
Question 2
A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?
Question 3
What is the OSPF metric called?
Question 4
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Question 5
A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?
Question 6
A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?
FAQ
Questions learners often ask
What does this 200-301 question test?
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?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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