CCNA IP Routing Practice Question
Exhibit
R1# show ip ospf database summary
OSPF Router with ID (192.168.1.1) (Process ID 1)
Summary Net Link States (Area 0)
LS age: 312
Options: (No TOS-capability, DC)
LS Type: Summary Links(Network)
Link State ID: 10.1.0.0 (summary Network Number)
Advertising Router: 10.1.1.1
LS Seq Number: 8000000A
Checksum: 0x1F3A
Length: 28
Network Mask: /16
MTID: 0 Metric: 1000
LS age: 467
Options: (No TOS-capability, DC)
LS Type: Summary Links(Network)
Link State ID: 10.2.0.0 (summary Network Number)
Advertising Router: 10.1.1.1
LS Seq Number: 80000005
Checksum: 0xA5C1
Length: 28
Network Mask: /16
MTID: 0 Metric: 10
LS age: 285
Options: (No TOS-capability, DC)
LS Type: Summary Links(Network)
Link State ID: 10.3.0.0 (summary Network Number)
Advertising Router: 10.1.1.1
LS Seq Number: 80000007
Checksum: 0x7F2B
Length: 28
Network Mask: /16
MTID: 0 Metric: 20Refer to the exhibit. A network engineer notices that traffic from R1 to the 10.1.0.0/16 network is taking a longer path than expected despite OSPF being the only routing protocol. The engineer examines the OSPF LSDB on R1 to investigate. Based on the output, what is the most likely cause of the suboptimal routing?
⚠ Common exam trap
Cisco often tests the distinction between route summarization with a fixed cost versus default OSPF cost calculation, and the trap here is that candidates may confuse the 'area range cost' command with external route metric manipulation or filtering, rather than recognizing it as a summary route cost override.
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 ABR is configured with the 'area 1 range 10.1.0.0 255.255.0.0 cost 1000' command.
The OSPF LSDB output shows that the route to 10.1.0.0/16 has a metric of 1000, which is unusually high for an intra-area or inter-area route. The 'area 1 range 10.1.0.0 255.255.0.0 cost 1000' command on the ABR sets a fixed cost for the summarized route, overriding the default OSPF cost calculation. This causes R1 to see a higher metric for the summarized route, leading to suboptimal routing if a lower-cost path exists via another area or router.
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 reference bandwidth has been misconfigured on R1, causing the OSPF cost calculation to be inflated for some links.
Why it's wrong here
A misconfigured reference bandwidth would affect the metric of all LSAs originated by or received on R1, but other summary LSAs from the same ABR show normal metrics. Additionally, reference bandwidth changes only impact local interface costs, not the metric carried in an LSA originated by another router.
- ✗
The ABR is filtering the 10.1.0.0/16 route from Area 1 into Area 0, causing the router to recalculate the metric higher.
Why it's wrong here
Route filtering with a distribute-list or prefix-list prevents the LSA from being advertised; it does not modify the metric. A filtered route would not appear in the LSDB at all, not appear with an inflated metric.
- ✓
The ABR is configured with the 'area 1 range 10.1.0.0 255.255.0.0 cost 1000' command.
Why this is correct
The ABR (10.1.1.1) is advertising a Type 3 summary LSA for 10.1.0.0/16 with a metric of 1000. This matches the behavior of the 'area range' command with the 'cost' keyword, which overrides the default metric calculation for inter-area summaries and injects the specified cost. The other LSAs from the same ABR use normal metrics, confirming the summary-specific configuration.
- ✗
The metric-type for OSPF external routes has been set to type 2, causing the metric to be inflated to 1000 for the 10.1.0.0/16 prefix.
Why it's wrong here
External routes are advertised in Type 5 LSAs (or Type 7 in NSSA), not Type 3 summary LSAs. The metric type (E1 vs E2) does not apply to inter-area summary routes. The exhibit clearly shows 'Summary Net Link States' (Type 3), so external route metric type is irrelevant.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓The ABR is configured with the 'area 1 range 10.1.0.0 255.255.0.0 cost 1000' command.Correct answer▾
Why this is correct
The ABR (10.1.1.1) is advertising a Type 3 summary LSA for 10.1.0.0/16 with a metric of 1000. This matches the behavior of the 'area range' command with the 'cost' keyword, which overrides the default metric calculation for inter-area summaries and injects the specified cost. The other LSAs from the same ABR use normal metrics, confirming the summary-specific configuration.
✗The reference bandwidth has been misconfigured on R1, causing the OSPF cost calculation to be inflated for some links.Wrong answer — click to see why▾
Why this is wrong here
Candidates may attribute arbitrary high metrics to a bandwidth calculation error, without noticing that only one LSA is affected.
✗The ABR is filtering the 10.1.0.0/16 route from Area 1 into Area 0, causing the router to recalculate the metric higher.Wrong answer — click to see why▾
Why this is wrong here
A misunderstanding that filtering can somehow alter the metric rather than block the advertisement completely.
✗The metric-type for OSPF external routes has been set to type 2, causing the metric to be inflated to 1000 for the 10.1.0.0/16 prefix.Wrong answer — click to see why▾
Why this is wrong here
Confusion between external and inter-area route types leads candidates to think that metric-type manipulation could affect an internal summary LSA.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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
OSPFv3 Single-Area Configuration for IPv6
Key term
LSDB
The Link State Database is a table maintained by OSPF routers that stores the complete network topology, including all links and routers, to calculate the best paths.
Key term
OSPF
OSPF is a link-state routing protocol used to find the best path for data packets to travel across IP networks, like a smart GPS that recalculates routes when traffic changes.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 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 200-301 exam.