CCNA IP Routing Practice Question
Exhibit
R1 G0/0: 10.12.12.1/30, ip ospf 1 area 0 R2 G0/0: 10.12.12.2/30, ip ospf 1 area 1 Both interfaces are up/up.
R1 and R2 are directly connected. Their interfaces are up/up and belong to the same subnet. R1's OSPF configuration places the interface in area 0, while R2's interface is in area 1. R1 does not show R2 as an OSPF neighbor. What is the most likely cause?
⚠ Common exam trap
A common trap is focusing on router ID or subnet mask instead of recognizing that mismatched area IDs prevent OSPF adjacency.
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 IDs do not match
OSPF neighbors on the same link must agree on the area ID. Here, one side is in area 0 and the other is in area 1, so adjacency never forms even though the interfaces are up and in the same subnet.
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 area IDs do not match
Why this is correct
Each OSPF interface must be assigned to the same area on both ends of a link. The Hello packet carries the originating router's area ID, and a receiving router checks this value against its own; a mismatch causes the Hello to be silently discarded, leaving the neighbor list empty. Even with correct IP addressing and timers, a mismatch in area IDs prevents the OSPF adjacency from ever reaching the two-way state.
- ✗
R1 must use a loopback as the router ID
Why it's wrong here
An OSPF router ID is derived from the highest active loopback IP, or if none exists, from the highest IP on a non-loopback interface; a loopback interface is not required for OSPF operation. The routers can form an adjacency with any valid router ID, provided the area IDs match, so the missing neighbor is not caused by the lack of a loopback interface.
When this WOULD be correct
In a different scenario where the question specifies that OSPF requires a router ID to be explicitly set and that the router ID must be a loopback address, this option would be correct. For example, if the question stated that R1 must use a loopback interface for OSPF to establish neighbor relationships, then this option would apply.
- ✗
The subnet mask is too small for OSPF to work
Why it's wrong here
OSPF does not impose a minimum prefix length; a /30 is specifically designed for point-to-point links and is fully supported. The problem lies elsewhere, as adjacency formation depends on matching area IDs, timers, and authentication, not on the mask's size.
When this WOULD be correct
In a different scenario, if a question specified that R1 and R2 are on the same subnet but have mismatched subnet masks that prevent them from being in the same broadcast domain, then a small subnet mask could indeed be the reason for OSPF not establishing a neighbor relationship.
- ✗
R2 should be configured as the DR manually
Why it's wrong here
DR/BDR election only affects the exchange of LSAs on multi-access networks, not the formation of a two-way neighbor state. Since R1 and R2 are directly connected on a point-to-point link, no DR election takes place, and manually forcing R2 as DR would not solve a missing neighbor that stems from an area mismatch.
When this WOULD be correct
In a different scenario where the question specifies a multi-access network with multiple OSPF routers, and the exam asks about ensuring a specific router is elected as the DR, this option would be correct if the manual configuration of DR is required to meet specific network design criteria.
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 IDs do not matchCorrect answer▾
Why this is correct
Each OSPF interface must be assigned to the same area on both ends of a link. The Hello packet carries the originating router's area ID, and a receiving router checks this value against its own; a mismatch causes the Hello to be silently discarded, leaving the neighbor list empty. Even with correct IP addressing and timers, a mismatch in area IDs prevents the OSPF adjacency from ever reaching the two-way state.
✗R1 must use a loopback as the router IDWrong answer — click to see why▾
Why this is wrong here
OSPF does not require a loopback interface as the router ID; any IP address on an active interface can be used, or the router ID can be manually configured. A loopback is recommended for stability but is not mandatory for forming neighbor relationships.
★ When this WOULD be the correct answer
In a different scenario where the question specifies that OSPF requires a router ID to be explicitly set and that the router ID must be a loopback address, this option would be correct. For example, if the question stated that R1 must use a loopback interface for OSPF to establish neighbor relationships, then this option would apply.
Why candidates choose this
Students often hear that loopback interfaces are best practice for OSPF router IDs and may mistakenly believe they are required. This confusion arises because many study materials emphasize using loopbacks for stability, leading to the incorrect assumption that OSPF will not work without one.
✗The subnet mask is too small for OSPF to workWrong answer — click to see why▾
Why this is wrong here
A /30 subnet mask (255.255.255.252) provides two usable host addresses, which is perfectly sufficient for a point-to-point link between two routers. OSPF works correctly with any valid subnet mask, including /30.
★ When this WOULD be the correct answer
In a different scenario, if a question specified that R1 and R2 are on the same subnet but have mismatched subnet masks that prevent them from being in the same broadcast domain, then a small subnet mask could indeed be the reason for OSPF not establishing a neighbor relationship.
Why candidates choose this
Some students think OSPF requires a larger subnet (e.g., /24) because they confuse OSPF's network type requirements with other protocols or assume that a small subnet might cause issues. However, OSPF operates fine on point-to-point links with /30 masks.
✗R2 should be configured as the DR manuallyWrong answer — click to see why▾
Why this is wrong here
On a point-to-point link, OSPF does not use a Designated Router (DR) or Backup Designated Router (BDR); the neighbor relationship forms directly without election. Manually configuring a DR is unnecessary and would not affect adjacency formation.
★ When this WOULD be the correct answer
In a different scenario where the question specifies a multi-access network with multiple OSPF routers, and the exam asks about ensuring a specific router is elected as the DR, this option would be correct if the manual configuration of DR is required to meet specific network design criteria.
Why candidates choose this
Students may recall that OSPF uses DR/BDR on multiaccess networks (like Ethernet) and incorrectly assume that DR election is always required. They might think that without a DR, OSPF cannot form neighbors, but this only applies to broadcast or NBMA networks, not point-to-point links.
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
Area 0
Area 0 is the backbone area in OSPF routing that connects all other OSPF areas to ensure a loop-free and efficient network routing 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.