CCNA IP Routing Practice Question
After configuring the area 0 range 10.0.0.0 255.255.0.0 command on an OSPF ABR, a technician finds that a host at 10.0.5.100 in Area 1 cannot reach hosts in Area 0. The ABR’s OSPF database shows only the summary 10.0.0.0/16 in Area 0, and no individual /24 routes. What is the most likely cause?
⚠ Common exam trap
Cisco often tests the misconception that the `area range` command only summarizes routes without suppressing the more-specific LSAs, leading candidates to incorrectly attribute the connectivity loss to filtering or routing issues rather than the intended suppression behavior.
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 area range command causes the ABR to advertise only the summary LSA and suppress the more-specific Type-3 LSAs for the range.
The `area 0 range 10.0.0.0 255.255.0.0` command on an OSPF ABR creates a single Type-3 summary LSA (10.0.0.0/16) for Area 0 and suppresses the advertisement of more-specific Type-3 LSAs (e.g., /24 routes) that fall within that range. This is the intended behavior of the `range` command: it summarizes routes at the ABR and prevents the individual component routes from being advertised into the backbone area. Since the host at 10.0.5.100 in Area 1 relies on those specific /24 routes to reach destinations in Area 0, the suppression breaks connectivity.
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 ABR is filtering the specific /24 routes using a distribute-list under the OSPF process.
Why it's wrong here
The ABR is not applying any distribute-list in the OSPF configuration; the scenario shows no such filter. Distribute-lists under OSPF are used to filter routing updates in and out, but they would not produce the exact suppression of specific /24 routes when an area range is active. The observed reduction in Type-3 LSAs is the default behavior of the area range command, which summarizes the range and automatically suppresses the individual component routes from being advertised into Area 0. Therefore, this option is incorrect.
- ✗
The routers in Area 1 are no longer advertising their /24 routes to the ABR because the ABR is in a different area.
Why it's wrong here
OSPF routers in Area 1 continue to flood their Type-1 LSAs to the ABR, which then converts them to Type-3 LSAs. The ABR receives all /24 routes before summarization occurs, so this is not the cause.
- ✓
The area range command causes the ABR to advertise only the summary LSA and suppress the more-specific Type-3 LSAs for the range.
Why this is correct
By default, the area range command summarizes the specified prefix range and suppresses the individual component routes from being advertised into the target area. Only the summary LSA appears in Area 0, which matches the observed behavior.
- ✗
The ABR has automatically created a discard route to null0 for the summary, which is dropping all traffic destined to the summarized networks.
Why it's wrong here
Although a discard route for 10.0.0.0/16 is installed on the ABR to prevent routing loops, it only discards traffic when no more-specific route matches. Since the ABR still has the /24 routes from Area 1, traffic to 10.0.5.100 is forwarded using the longer match and is not dropped.
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 area range command causes the ABR to advertise only the summary LSA and suppress the more-specific Type-3 LSAs for the range.Correct answer▾
Why this is correct
By default, the area range command summarizes the specified prefix range and suppresses the individual component routes from being advertised into the target area. Only the summary LSA appears in Area 0, which matches the observed behavior.
✗The ABR is filtering the specific /24 routes using a distribute-list under the OSPF process.Wrong answer — click to see why▾
Why this is wrong here
A distribute-list requires explicit configuration; its absence makes this an unsubstantiated guess.
✗The routers in Area 1 are no longer advertising their /24 routes to the ABR because the ABR is in a different area.Wrong answer — click to see why▾
Why this is wrong here
Area border routers receive all LSAs from non-backbone areas; the area boundary does not stop LSA propagation to the ABR itself.
✗The ABR has automatically created a discard route to null0 for the summary, which is dropping all traffic destined to the summarized networks.Wrong answer — click to see why▾
Why this is wrong here
The null0 route is a loop-prevention mechanism, not an absolute traffic blocker; more-specific entries in the routing table take precedence.
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
OSPF
OSPF is a link-state routing protocol that uses the SPF algorithm to compute the shortest path to each destination within a single autonomous system.
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.