hardMultiple ChoiceObjective-mapped
300-410 Practice Question: Is troubleshooting an OSPFv3 issue where a router…
A network engineer is troubleshooting an OSPFv3 issue where a router R1 is not learning routes from a neighbor R2. The adjacency is FULL, but 'show ipv6 route ospf' on R1 shows only a default route. R2 is an ASBR redistributing connected routes into OSPFv3. 'show ipv6 ospf database external' on R1 shows the external routes, but they are not installed in the routing table. What is the most likely cause?
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 router R1 has a distribute-list in the OSPFv3 process that filters out the external routes.
In OSPFv3, external routes are not installed if the router has a route to the forwarding address that is not reachable. However, the more common cause is that the OSPFv3 process on R1 has 'no ipv6 unicast-routing' or the router is missing a default route to reach the external destinations. Another possibility is that the external routes have a metric that is too high or the route is suppressed by a filter. The most likely cause is that the router has a route map or distribute list that is filtering the external routes from being installed.
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 router R1 has a distribute-list in the OSPFv3 process that filters out the external routes.
Why this is correct
A distribute-list can filter routes from being installed in the routing table even if they are in the LSDB.
- ✗
The external routes have a metric of 16777214, which is considered infinite.
Why it's wrong here
While a metric that high could prevent installation, it is not typical for redistributed connected routes.
- ✗
The router R1 does not have IPv6 unicast routing enabled.
Why it's wrong here
If IPv6 unicast routing were disabled, OSPFv3 would not form adjacencies or install any routes.
- ✗
The external routes are type 5 LSAs but the router is in a totally stubby area.
Why it's wrong here
Totally stubby areas block type 5 LSAs entirely, so they would not appear in the database.
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
Introduction to ENARSI Exam and Network Fundamentals
Key term
Policy Based Routing
Policy Based Routing (PBR) is a technology that allows network traffic to be forwarded based on user-defined policies rather than just the destination IP address in 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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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.