CCNA IP Routing Practice Question
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?
⚠ Common exam trap
Focus on OSPFv3 configuration requirements like area matching, not on distractors such as hostnames or prefix length.
Answer choices
Why each option matters
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.
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
OSPFv3 requires that all routers on the same link share the same area ID; if one interface belongs to area 0 and the other to area 1, the Area ID field in the Hello packet doesn't match, and the packet is silently dropped. The neighbor state stays in DOWN because OSPFv3 cannot form an adjacency when the area numbers are different. This is a core OSPF principle: neighbors must be configured with the same area on the connecting link.
- ✗
The routers need matching hostnames before OSPFv3 can start.
Why it's wrong here
Hostnames are purely informational labels and are never transmitted in OSPFv3 Hellos or used in the neighbor selection process. OSPFv3 adjacency depends on matching Router ID, area ID, timers, and optional authentication; hostname configuration has no effect on these parameters. Therefore, two routers with different hostnames can still become OSPFv3 neighbors if all protocol parameters are correctly set.
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
The claim that IPv6 requires a /64 only for routing protocols is incorrect because OSPFv3 works with any IPv6 prefix length; routing protocols do not mandate a particular subnet mask. The routers' inability to form an adjacency is best explained by a mismatch in OSPFv3 configuration, such as different area IDs, not by the prefix length. A /64 is commonly used for network addressing but is not a protocol requirement for adjacency.
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
OSPFv3 is explicitly designed to run on directly connected IPv6 interfaces; it uses a shared link to exchange Hello and database packets, so a point-to-point connection between two routers is a typical and fully supported deployment. If the routers cannot form an adjacency, the cause is not that the interfaces are directly connected, but rather some misconfiguration such as mismatched areas, timers, or wrong instance ID. Direct connectivity is a precondition, not an obstacle.
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
OSPFv3 requires that all routers on the same link share the same area ID; if one interface belongs to area 0 and the other to area 1, the Area ID field in the Hello packet doesn't match, and the packet is silently dropped. The neighbor state stays in DOWN because OSPFv3 cannot form an adjacency when the area numbers are different. This is a core OSPF principle: neighbors must be configured with the same area on the connecting link.
✗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?”
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
Go deeper
Related to this question
Learn chapter
OSPFv3 Single-Area Configuration for IPv6
Key term
OSPFv3
OSPFv3 is the version of the Open Shortest Path First routing protocol that supports IPv6 networks, enabling routers to exchange routing information for IPv6 addresses.
Key term
OSPF
OSPF is a link-state routing protocol used to find the best path for data packets to travel across IP networks, like a smart GPS that recalculates routes when traffic changes.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.