CCNA IP Routing Practice Question
Exhibit
R1# show running-config | section router ospf router ospf 1 router-id 1.1.1.1 network 203.0.113.0 0.0.0.3 area 0 network 203.0.113.128 0.0.0.0 area 0 passive-interface Loopback0 R1# show ip ospf neighbor R1# show ip ospf interface gigabitethernet 0/0 GigabitEthernet0/0 is up, line protocol is up Internet Address 203.0.113.1/30, Area 0 Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 1 Transmit Delay is 1 sec, State WAITING, Priority 1 No Hellos (Passive interface) R2# show running-config | section router ospf router ospf 1 router-id 2.2.2.2 network 203.0.113.0 0.0.0.3 area 0
You are connected to R1 via the console. Configure single-area OSPFv2 on R1 and R2 so that they form a full adjacency. The link between R1 and R2 uses 203.0.113.0/30. R1 has G0/0 203.0.113.1/30 and R2 has G0/0 203.0.113.2/30. R1's router-id must be 1.1.1.1, and R2's router-id must be 2.2.2.2. R1's GigabitEthernet0/0 interface is configured as a passive interface under OSPF, preventing OSPF hello messages from being sent out of that interface. Ensure that R1 does not send OSPF hellos out of its loopback0 interface (203.0.113.129/32). After configuration, verify the adjacency is established and OSPF routes are exchanged.
⚠ Common exam trap
The trap is that candidates may overlook the 'passive-interface' command's effect on hello suppression. They might focus on router-id or subnet issues instead. Always check 'show ip ospf interface' for passive status when adjacency fails.
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 adjacency fails because R1's GigabitEthernet0/0 interface is configured as passive-interface. Remove the passive-interface command for G0/0.
The adjacency fails because R1's GigabitEthernet0/0 interface is configured as passive-interface (the 'No Hellos' line in show ip ospf interface). This prevents R1 from sending OSPF hellos to R2. To fix, remove the passive-interface command for G0/0. The loopback0 interface should remain passive. After removal, verify with 'show ip ospf neighbor' to see the neighbor state change to FULL and 'show ip route ospf' to see routes.
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 adjacency fails because R1's GigabitEthernet0/0 interface is configured as passive-interface. Remove the passive-interface command for G0/0.
Why this is correct
In OSPF, configuring an interface with passive-interface suppresses OSPF hello packets on that interface, so R1's G0/0 never sends hellos to R2. Without a hello exchange, OSPF cannot discover neighbors or form an adjacency, even though the connected network is still advertised. Removing passive-interface on G0/0 restores hello transmission and allows the adjacency with R2 to come up; loopback0 can stay passive because its route is still injected into OSPF.
- ✗
The adjacency fails because the router-id 1.1.1.1 is not reachable from R2. Configure a static route for 1.1.1.1/32 on R2.
Why it's wrong here
The OSPF router-id is simply a 32-bit identifier drawn from the highest loopback or configured manually; it is not an address that OSPF uses for packet forwarding. R2 does not need to have a route to 1.1.1.1/32 because OSPF neighbor packets are sourced from the physical interface IP address, not the router-id. Adding a static route for the router-id would have no effect on hello processing, and the real cause of the failure is R1's passive-interface command.
- ✗
The adjacency fails because the subnet mask on the link is /30 but OSPF expects a /24. Change the mask to /24 on both interfaces.
Why it's wrong here
This is incorrect because OSPF does not require a specific subnet mask; it can form adjacency over any mask as long as the interfaces are in the same subnet. A /30 is perfectly valid for point-to-point links.
- ✗
The adjacency fails because OSPF is not enabled on R2's GigabitEthernet0/0 interface. Configure 'ip ospf 1 area 0' on R2's G0/0.
Why it's wrong here
This is incorrect because the question implies both routers are configured for OSPF; the issue is specifically on R1's passive-interface. If OSPF were not enabled on R2's interface, there would be no hello packets at all, but the scenario shows R1 is not sending hellos.
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 adjacency fails because R1's GigabitEthernet0/0 interface is configured as passive-interface. Remove the passive-interface command for G0/0.Correct answer▾
Why this is correct
In OSPF, configuring an interface with passive-interface suppresses OSPF hello packets on that interface, so R1's G0/0 never sends hellos to R2. Without a hello exchange, OSPF cannot discover neighbors or form an adjacency, even though the connected network is still advertised. Removing passive-interface on G0/0 restores hello transmission and allows the adjacency with R2 to come up; loopback0 can stay passive because its route is still injected into OSPF.
✗The adjacency fails because the router-id 1.1.1.1 is not reachable from R2. Configure a static route for 1.1.1.1/32 on R2.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that router-ids are not required to be routable; they are merely identifiers within the OSPF domain.
Why candidates choose this
Candidates might think that since router-id is an IP address, it must be reachable for OSPF to work, confusing it with a loopback interface used for BGP or other protocols.
✗The adjacency fails because the subnet mask on the link is /30 but OSPF expects a /24. Change the mask to /24 on both interfaces.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that OSPF has no mask requirement beyond matching subnet; /30 is commonly used for serial links.
Why candidates choose this
Candidates might recall that some routing protocols (like RIPv2) have issues with certain masks, or confuse OSPF network types (point-to-point vs broadcast) with mask requirements.
✗The adjacency fails because OSPF is not enabled on R2's GigabitEthernet0/0 interface. Configure 'ip ospf 1 area 0' on R2's G0/0.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error is that the problem is on R1's side, not R2's. R2's interface is likely enabled but not receiving hellos from R1.
Why candidates choose this
Candidates often check both sides for OSPF enablement and might assume R2 is misconfigured, especially if they see 'show ip ospf neighbor' showing nothing.
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 neighbor
An OSPF neighbor is another router that has been directly discovered through OSPF Hello packets and is willing to exchange routing information to build a network topology map.
Key term
Passive interface
A passive interface is a network interface that participates in a routing protocol (like OSPF) by listening for and learning routes, but does not send routing protocol messages out of that interface.
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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.