hardMultiple ChoiceObjective-mapped
OSPF Route Summarization: Troubleshooting ABR and Network Type Issues
OSPF network type mismatch on a multi-access link is causing route summarization issues. Router R1 and R2 are connected via Ethernet, but R1 has:
interface GigabitEthernet0/0 ip address 10.0.0.1 255.255.255.0 ip ospf network point-to-point ip ospf 1 area 0
!
Router R2 has default OSPF network type (broadcast). R1 is configured with: router ospf 1 area 0 range 10.0.0.0 255.255.255.0
! R2 shows:
R2# show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.0.0.1 0 FULL/ - 00:00:30 10.0.0.1 GigabitEthernet0/0
But R2 does not have the summary route in its routing table. What is the root cause?
Quick Answer
The answer is that R1 is not an ABR, so the area 0 range command does not generate a summary route. The OSPF route summarization feature only works on an ABR (connecting area 0 to a non-zero area) or an ASBR, and since R1 has all interfaces in area 0, it has no inter-area routes to summarize. The network type mismatch between R1’s point-to-point and R2’s broadcast does cause DR/BDR election issues and can disrupt LSA flooding, but the neighbor state shows FULL, meaning the adjacency is technically up—the real root cause is the missing ABR role. On the Cisco CCNP ENARSI 300-410 exam, this question tests your understanding that the area range command is not a magic bullet; it only takes effect when the router is summarizing routes between areas. A common trap is to blame the network type mismatch or assume the summary is automatically generated, but the key insight is that a single-area OSPF configuration cannot produce inter-area summaries. Memory tip: “No ABR, no area range—summaries need a border to exchange.”
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
✓
R1 is not an ABR (only area 0), so the area range command does not generate a summary route.
The network type mismatch (point-to-point on R1, broadcast on R2) prevents proper adjacency formation. Although the neighbor state shows FULL, the DR/BDR election is affected. R1's point-to-point setting means it does not participate in DR election, and R2 expects a DR. This can cause LSA flooding issues, and the area range summary may not be advertised correctly. The summary route is generated by the ABR, but if R1 is not an ABR (area 0 only), the range command has no effect. The root cause is that R1 is not an ABR, so area range does not apply.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
R1 is not an ABR (only area 0), so the area range command does not generate a summary route.
Why this is correct
Area range only works on ABRs that connect multiple areas.
- ✗
The network type mismatch causes OSPF to not exchange LSAs correctly, preventing the summary.
Why it's wrong here
The adjacency is FULL, so LSAs are exchanged.
- ✗
The summary route is suppressed because the interface is point-to-point.
Why it's wrong here
Point-to-point does not suppress summarization.
- ✗
R2 has a static route that overrides the summary.
Why it's wrong here
No static route is indicated.
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
About these practice questions
This 300-410 question is part of Courseiva's 1,966-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more way this is tested on 300-410
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which OSPF LSA type is used to advertise a summary route for a network outside the area but within the same OSPF domain?
medium- A.Type 1
- B.Type 2
- ✓ C.Type 3
- D.Type 5
Why C: Type 3 LSAs (Summary LSAs) are generated by Area Border Routers (ABRs) to advertise inter-area routes.
JA
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.