CCNA IP Routing Practice Question
Exhibit
R1# show ip route ospf
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override
Gateway of last resort is not set
192.168.10.0/24 is variably subnetted, 2 subnets, 2 masks
O 192.168.10.0/24 [110/2] via 10.1.1.2, 00:35:14, GigabitEthernet0/1
192.168.20.0/24 is variably subnetted, 2 subnets, 2 masks
O 192.168.20.0/24 [110/2] via 10.1.1.2, 00:35:14, GigabitEthernet0/1
R1#Refer to the exhibit. A network engineer is troubleshooting a missing route on R1. The router R3 is configured to advertise network 192.168.30.0/24 via OSPF, but the route is not present in the OSPF routing table of R1 when issuing the show ip route ospf command. What is the most likely cause?
⚠ Common exam trap
Cisco often tests the passive-interface default behavior where candidates assume that configuring OSPF with a network statement is sufficient to form adjacencies, overlooking that passive-interface default silently blocks hello packets on all interfaces unless explicitly overridden.
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
✓
R3 has passive-interface default configured and has not issued the no passive-interface command on the interface facing the OSPF neighbor.
R3 has passive-interface default configured, which makes all interfaces passive by default, preventing OSPF hello packets from being sent. Without the no passive-interface command on the interface facing R1, R3 cannot form an OSPF adjacency, so R1 never learns the 192.168.30.0/24 route. This is a common misconfiguration when using passive-interface default to suppress OSPF on non-neighbor interfaces.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
R3 has not enabled OSPF on the network 192.168.30.0/24 using the network command.
Why it's wrong here
While omitting the `network 192.168.30.0 0.0.0.255 area 0` statement on R3 would also prevent the 192.168.30.0/24 route from being inserted into the OSPF database and advertised, the scenario explicitly states that R3 is already configured to advertise this network. In OSPF, the `network` command only places the interface into an OSPF area and determines whether outgoing hello packets are generated on that interface; it does not override the `passive-interface default` setting. Since the configuration includes the required network statement, the missing route cannot be attributed to an absent `network` command—the actual cause is that R3's `passive-interface default` is suppressing hello packets on the interface toward R1, preventing adjacency formation.
- ✓
R3 has passive-interface default configured and has not issued the no passive-interface command on the interface facing the OSPF neighbor.
Why this is correct
Passive-interface default suppresses OSPF hello packets on all interfaces unless explicitly enabled. Without hellos, an adjacency cannot form, so R1 never learns the 192.168.30.0/24 route. The exhibit shows OSPF working with another neighbor, confirming the problem is isolated to R3’s interface configuration.
- ✗
R1 has an inbound ACL applied to GigabitEthernet0/1 that blocks OSPF multicast traffic to 224.0.0.5 and 224.0.0.6.
Why it's wrong here
If such an ACL existed, R1 would not be able to form any OSPF adjacency on that interface, yet the exhibit shows R1 has learned 192.168.10.0/24 and 192.168.20.0/24 via the same GigabitEthernet0/1. This proves OSPF multicast traffic is being received and processed correctly.
- ✗
R3's OSPF router ID is duplicated with another OSPF router, causing the SPF algorithm to drop routes.
Why it's wrong here
A duplicate router ID can cause adjacency flapping or failure to establish, but if hellos are still exchanged, an adjacency might form temporarily. However, this issue would typically affect all routes from that router, and the exhibit shows no route from R3 at all, which points more directly to an adjacency never forming because hellos were never sent (passive-interface). Moreover, the OSPF neighbor table would show the neighbor in a problematic state, but we are given only the routing table; the passive-interface scenario cleanly explains the missing route without conflicting with observable facts.
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.
✓R3 has passive-interface default configured and has not issued the no passive-interface command on the interface facing the OSPF neighbor.Correct answer▾
Why this is correct
Passive-interface default suppresses OSPF hello packets on all interfaces unless explicitly enabled. Without hellos, an adjacency cannot form, so R1 never learns the 192.168.30.0/24 route. The exhibit shows OSPF working with another neighbor, confirming the problem is isolated to R3’s interface configuration.
✗R3 has not enabled OSPF on the network 192.168.30.0/24 using the network command.Wrong answer — click to see why▾
Why this is wrong here
The question says R3 advertises the network via OSPF; a missing network command would contradict that, so the failure must be in adjacency formation.
✗R1 has an inbound ACL applied to GigabitEthernet0/1 that blocks OSPF multicast traffic to 224.0.0.5 and 224.0.0.6.Wrong answer — click to see why▾
Why this is wrong here
The presence of other OSPF routes on the same interface disproves a blanket multicast ACL; the issue is specific to R3’s adjacency.
✗R3's OSPF router ID is duplicated with another OSPF router, causing the SPF algorithm to drop routes.Wrong answer — click to see why▾
Why this is wrong here
A duplicate router ID could prevent adjacency, but the scenario’s focus on passive-interface default provides a more common and direct cause for a total lack of adjacency when OSPF is correctly configured on the network.
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
Route
A route is a path that data takes through a network from one device or network to another, determined by routing protocols and configured rules.
Key term
Routing table
A routing table is a data set stored in a router or host that contains information about network paths and is used to determine where to forward data packets.
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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.