300-410 Layer 3 Technologies Practice Question
A network engineer is deploying DMVPN Phase 3 with OSPF over the tunnel interface. The hub router must summarize all spoke routes into a single /24 prefix before advertising them into the corporate OSPF domain. The engineer configures `area 0 range 10.10.0.0 255.255.255.0` on the hub's ABR. After applying the configuration, spoke routes are still advertised individually. Which action resolves the issue?
⚠ Common exam trap
The trap here is assuming that the `area range` command works on any router regardless of its ABR status, when it only generates summary LSAs on a router that is an ABR for the specified area.
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
✓
Ensure the hub router is an ABR by placing the tunnel interface in a different area than the corporate domain, then apply the `area X range` command for that area.
Inter-area route summarization in OSPF requires the router to be an ABR, meaning it must have interfaces in at least two areas. The `area range` command only takes effect on an ABR for routes from the specified area. If the hub's tunnel and corporate interfaces are in the same area, no summary LSA is generated, so the spoke routes are advertised individually.
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 `ip ospf database-filter all out` on the hub tunnel interface to suppress individual LSAs and allow the summary to propagate.
Why it's wrong here
The `database-filter` command blocks LSA flooding on an interface but does not create summary LSAs. It would prevent spoke routes from being advertised at all, not summarize them. Summarization is an ABR function configured with `area range`, so this command cannot achieve the desired single-prefix advertisement.
- ✗
Configure the `area 0 range 10.10.0.0 255.255.255.0` command on the hub router's tunnel interface instead of the global OSPF process.
Why it's wrong here
The `area range` command is entered under the OSPF routing process, not on an interface. Placing it under the tunnel interface is invalid syntax and would be rejected. Interface-level OSPF commands control timers, authentication, and network type, but not inter-area summarization. This action cannot produce the required summary LSA.
- ✗
Change the OSPF network type on the hub tunnel interface to point-to-multipoint and reapply the `area 0 range` command.
Why it's wrong here
Changing the network type affects neighbor formation and next-hop behavior but does not enable summarization. Summarization requires the router to be an ABR for the area containing the routes. The network type is irrelevant to the ABR requirement, so this action leaves the underlying problem unresolved and spoke routes remain individual.
- ✓
Ensure the hub router is an ABR by placing the tunnel interface in a different area than the corporate domain, then apply the `area X range` command for that area.
Why this is correct
OSPF area summarization is performed by an ABR on routes entering the backbone. If the tunnel interface belongs to the same area as the corporate domain, the hub is not an ABR and cannot generate summary LSAs. Placing the tunnel in a separate area makes the hub an ABR, allowing `area X range` to summarize spoke routes before advertising 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.
Go deeper
Related to this question
Learn chapter
BGP Route Selection and Policy
Key term
BGP Route Aggregation
BGP Route Aggregation is a technique that combines multiple specific network routes into a single summary route to reduce the size of routing tables and improve network efficiency.
Key term
DMVPN Phase 3
DMVPN Phase 3 is a Cisco networking technology that allows branch offices to connect directly to each other without always going through a central hub, but with smarter routing that lets the hub control the traffic paths more efficiently.
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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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