CCNA IP Routing Practice Question
Exhibit
R1# interface GigabitEthernet0/0 ip address 10.1.12.1 255.255.255.0 ip ospf authentication message-digest ip ospf message-digest-key 1 md5 cisco123 ! router ospf 10 network 10.1.12.0 0.0.0.255 area 0 R2# interface GigabitEthernet0/0 ip address 10.1.12.2 255.255.255.0 ! router ospf 10 network 10.1.12.0 0.0.0.255 area 0
R1 and R2 are directly connected. Both are configured in OSPF area 0, and they can successfully ping each other. However, OSPF neighbor adjacency fails. R1's interface is configured with `ip ospf authentication message-digest` and a valid key, while R2's interface has no OSPF authentication configured. What is the most likely cause?
⚠ Common exam trap
A frequent exam trap is assuming that successful ping and matching OSPF areas guarantee neighbor adjacency. Candidates often overlook OSPF authentication mismatches, especially when one router uses message-digest authentication and the other does not. This leads to confusion because the link appears operational at Layer 3, but OSPF packets are discarded silently. The trap exploits the misconception that IP connectivity alone is sufficient for OSPF adjacency, ignoring the protocol’s security requirements.
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 OSPF authentication settings do not match.
The most likely cause is an OSPF authentication mismatch. Although the routers have IP connectivity and are in the same OSPF area, OSPF adjacency requires matching security parameters. R1 uses message-digest authentication whereas R2 has none configured, preventing neighbor formation. The other options are incorrect: the stem confirms they are in the same area (A), OSPF does not require identical hostnames (C), and successful pings prove the subnet mask does not block multicast traffic (D).
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 routers are in different OSPF areas.
Why it's wrong here
OSPF neighbor adjacency requires the interfaces on each router to be in the same OSPF area. Here, both R1 and R2 have the connecting subnet placed into area 0, so they are not in different areas. A mismatch in area IDs would prevent the Hello packet exchange from forming a neighbor relationship, but that condition is not present in this scenario.
When this WOULD be correct
In a different scenario, if the question indicated that R1 and R2 were configured in different OSPF areas, such as Area 0 for R1 and Area 1 for R2, then this option would be correct as routers in different areas cannot form OSPF adjacencies.
- ✓
The OSPF authentication settings do not match.
Why this is correct
R1 has OSPF MD5 authentication configured for the interface, while R2 does not have matching `ip ospf authentication message-digest` configuration. As a result, R1's authenticated Hello packets are silently discarded by R2, so no neighbor adjacency forms despite the fact that the routers can ping each other. OSPF authentication requires identical types, key IDs, and passwords on both ends; any mismatch causes the Hellos to be ignored.
- ✗
The routers need identical hostnames before adjacency can form.
Why it's wrong here
OSPF neighbour adjacency does not require identical hostnames; it relies on matching authentication parameters, area IDs, and hello/dead intervals. The adjacency fails here because R2 lacks the `ip ospf authentication message-digest` configuration, so R1’s authenticated hellos are discarded. This option is tempting because some routing protocols, such as EIGRP, use hostnames for neighbour identification, but OSPF uses Router IDs derived from the highest IP address or a configured `router-id`.
When this WOULD be correct
In a different scenario where the question specifies that OSPF adjacency is failing due to a requirement for routers to have matching hostnames for a proprietary implementation or a specific vendor's OSPF configuration, this option would be correct.
- ✗
The subnet mask prevents OSPF multicast traffic.
Why it's wrong here
OSPF multicast traffic uses reserved addresses 224.0.0.5 and 224.0.0.6, and the subnet mask configured on an interface does not filter or block these multicast packets. The /24 mask in use is irrelevant to OSPF's ability to send or receive Hello packets, and since the routers can ping each other, basic IP connectivity is fine. The adjacency failure is not caused by the mask but by a higher-layer mismatch, such as authentication.
When this WOULD be correct
In a scenario where two routers are configured with different subnet masks on their directly connected interfaces, and the question specifically asks about OSPF adjacency issues related to subnet configurations, this option would be correct. For example, if one router is configured with a /24 mask and the other with a /30 mask, OSPF would fail to form an adjacency.
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 OSPF authentication settings do not match.Correct answer▾
Why this is correct
R1 has OSPF MD5 authentication configured for the interface, while R2 does not have matching `ip ospf authentication message-digest` configuration. As a result, R1's authenticated Hello packets are silently discarded by R2, so no neighbor adjacency forms despite the fact that the routers can ping each other. OSPF authentication requires identical types, key IDs, and passwords on both ends; any mismatch causes the Hellos to be ignored.
✗The routers are in different OSPF areas.Wrong answer — click to see why▾
Why this is wrong here
The exhibit shows both routers place the subnet into area 0, so they are in the same OSPF area. Different areas would prevent adjacency, but that is not the case here.
★ When this WOULD be the correct answer
In a different scenario, if the question indicated that R1 and R2 were configured in different OSPF areas, such as Area 0 for R1 and Area 1 for R2, then this option would be correct as routers in different areas cannot form OSPF adjacencies.
Why candidates choose this
Students often confuse OSPF area mismatch as a common cause of adjacency failure, and if they misread the exhibit, they might think the areas differ.
✗The routers need identical hostnames before adjacency can form.Wrong answer — click to see why▾
Why this is wrong here
OSPF adjacency does not require identical hostnames; hostnames are only used for identification and do not affect the OSPF neighbor state machine.
★ When this WOULD be the correct answer
In a different scenario where the question specifies that OSPF adjacency is failing due to a requirement for routers to have matching hostnames for a proprietary implementation or a specific vendor's OSPF configuration, this option would be correct.
Why candidates choose this
Some students might confuse OSPF with protocols like EIGRP where the router ID must be unique, but hostnames are not a factor in OSPF adjacency formation.
✗The subnet mask prevents OSPF multicast traffic.Wrong answer — click to see why▾
Why this is wrong here
The /24 subnet mask does not block OSPF multicast traffic (224.0.0.5 and 224.0.0.6). OSPF multicasts are sent regardless of the subnet mask on the interface.
★ When this WOULD be the correct answer
In a scenario where two routers are configured with different subnet masks on their directly connected interfaces, and the question specifically asks about OSPF adjacency issues related to subnet configurations, this option would be correct. For example, if one router is configured with a /24 mask and the other with a /30 mask, OSPF would fail to form an adjacency.
Why candidates choose this
Students might think that a non-default subnet mask could affect multicast delivery, but OSPF uses link-local multicast addresses that are not filtered by the subnet mask.
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 adjacency
An OSPF adjacency is a logical neighbor relationship formed between two OSPF routers that have completed a series of hello and database exchange processes, enabling them to share routing information and maintain a consistent view of the network topology.
About these practice questions
This 200-301 question is part of Courseiva's 1,389-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 →
JA
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.