300-410 Layer 3 Technologies Practice Question
A network engineer is troubleshooting a dual-stack Cisco IOS XE router that runs OSPFv3 for IPv6 and OSPFv2 for IPv4. IPv4 adjacencies form and routes are exchanged, but no OSPFv3 adjacencies form and no IPv6 routes appear. The engineer verifies that the interfaces have IPv6 addresses and that `ipv6 unicast-routing` is enabled. Which configuration step is most likely missing?
⚠ Common exam trap
The trap here is assuming OSPFv3 is enabled on interfaces simply because the OSPFv3 process exists and IPv6 routing is globally enabled.
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
✓
Enable OSPFv3 on the interfaces by adding them to an OSPFv3 process with the `ipv6 ospf 1 area 0` interface command.
OSPFv3 requires explicit interface activation; creating the process and enabling global IPv6 routing are not enough. The `ipv6 ospf <process-id> area <area-id>` interface command enables OSPFv3 on that link and triggers hello packets. Without it, no OSPFv3 neighbor relationships form, even though IPv6 addressing and forwarding are correctly configured. This is a common oversight when migrating from OSPFv2, where network statements under the process can enable interfaces indirectly.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Configure an IPv6 address on the OSPFv3 process using the `ipv6 address` command under `router ospfv3`.
Why it's wrong here
IPv6 addresses are configured on interfaces, not under the OSPFv3 routing process. The OSPFv3 process does not accept an `ipv6 address` command; it uses interface-level commands to enable OSPFv3 and relies on link-local addresses for neighbor communication. This option misplaces the configuration and would not resolve the missing adjacency, since the real problem is that OSPFv3 is not enabled on the interfaces.
- ✗
Configure an OSPFv3 router ID with the `router-id` command under the OSPFv3 process.
Why it's wrong here
A router ID is required for OSPFv3 to function, but if no router ID is manually set, the router automatically derives one from an IPv4 address or loopback. A missing router ID would typically generate an error and prevent the process from running, but the scenario says OSPFv2 adjacencies and routes are working, so a router ID likely exists. The more immediate issue is that OSPFv3 is not enabled on the interfaces.
- ✗
Enable IPv6 unicast routing globally with the `ipv6 unicast-routing` command.
Why it's wrong here
The scenario explicitly states that `ipv6 unicast-routing` is already enabled and interfaces have IPv6 addresses. Without global IPv6 unicast routing, the router would not forward IPv6 packets, but that is not the cause here. The missing piece is interface-level OSPFv3 activation, which is separate from global IPv6 routing and must be configured on each participating interface.
- ✓
Enable OSPFv3 on the interfaces by adding them to an OSPFv3 process with the `ipv6 ospf 1 area 0` interface command.
Why this is correct
OSPFv3 does not automatically enable on interfaces when the process is created; each interface must be explicitly enabled with `ipv6 ospf <process-id> area <area-id>` or by using `ipv6 ospf area` under the interface. Without this command, the router will not send or process OSPFv3 hellos, so no adjacency forms even though IPv6 addressing and unicast routing are configured correctly.
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
Device Management and Network Monitoring (SNMP, Syslog, NetFlow)
Key term
IPv6 Next Hop Resolution
IPv6 Next Hop Resolution is the process a router uses to determine the next router or destination device to which a packet should be forwarded, based on the destination IPv6 address and the routing table.
Key term
IPv6 Routing OSPFv3
OSPFv3 is a routing protocol that lets routers share information about how to reach destinations in an IPv6 network, updating routes automatically as the network changes.
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JA
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
This 300-410 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 300-410 exam.