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300-410 Practice Question: Which TWO statements correctly describe the…
Which TWO statements correctly describe the behavior of OSPFv3 when troubleshooting neighbor adjacency issues on a Cisco IOS-XE router? (Choose TWO.)
⚠ Common exam trap
300-410 often tests OSPFv3 specifics: candidates may think the router ID is 128-bit or that network type is global, but it's 32-bit and per-interface.
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
✓
OSPFv3 neighbor adjacencies are formed using the link-local IPv6 address of the neighbor.
Option A is correct because OSPFv3 forms neighbor adjacencies over IPv6 link-local addresses, which are used as the source and next-hop for Hello packets on the link. Option D is correct because the 'show ipv6 ospf neighbor' command output includes the neighbor's link-local address, which is essential when troubleshooting adjacency issues. Option B is incorrect because the OSPFv3 router ID is a 32-bit value, not 128-bit, and is typically derived from an IPv4 address or manually configured. Option C is incorrect because OSPFv3 is enabled on an interface with the 'ipv6 ospf <process-id> area <area-id>' command, while 'ipv6 router ospf' enters the OSPFv3 process configuration mode. Option E is incorrect because OSPFv3 network type is configured per interface, not globally under the OSPFv3 process.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
OSPFv3 neighbor adjacencies are formed using the link-local IPv6 address of the neighbor.
Why this is correct
OSPFv3 runs directly over IPv6 and uses each interface's link-local address as the source and destination for Hello packets, so adjacency formation depends on those link-local addresses rather than global addresses. This is why neighbours must share a common link, satisfying the troubleshooting scenario.
- ✗
The OSPFv3 router ID is a 128-bit value derived from the highest loopback IPv6 address.
Why it's wrong here
The OSPFv3 router ID is a 32-bit value formatted like an IPv4 address, not 128-bit, and it is not derived from an IPv6 loopback address. It must be manually configured or inherited from an IPv4 address. A 128-bit identifier describes the IPv6 address, not the router ID.
- ✗
The 'ipv6 router ospf' command is used to enable OSPFv3 on an interface.
Why it's wrong here
The 'ipv6 router ospf' command creates the OSPFv3 routing process in global configuration mode; interface participation requires 'ipv6 ospf <process-id> area <area-id>' under the interface. It is tempting because process creation is a genuine prerequisite, but that step alone leaves the interface without an OSPFv3 adjacency.
- ✓
The 'show ipv6 ospf neighbor' command displays the link-local address of each neighbor.
Why this is correct
The 'show ipv6 ospf neighbor' output lists each neighbour's link-local address in the Neighbor ID or interface column, since OSPFv3 forms adjacencies over link-local addresses. This lets engineers verify the exact address used for Hello exchange when diagnosing adjacency failures.
- ✗
OSPFv3 uses the network type configured under the OSPFv3 process globally, not per interface.
Why it's wrong here
OSPFv3 network type is configured per interface with 'ipv6 ospf network', not globally under the process; the stem's global claim contradicts IOS-XE behaviour. It is tempting because several OSPFv3 parameters, such as router-id and reference bandwidth, are indeed set process-wide, but network type is not among them.
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.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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