The answer is the neighbor on GigabitEthernet0/1 stuck in the 2WAY/DROTHER state, which is the only adjacency not reaching FULL. In OSPF, the 2WAY state is a normal and stable condition for DROTHER routers on a broadcast multi-access network, indicating that two-way communication is established but the router is neither the Designated Router (DR) nor the Backup Designated Router (BDR). Because only DR and BDR routers form FULL adjacencies with all neighbors, DROTHER routers remain in 2WAY with each other, meaning they do not exchange Link State Advertisements directly. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of OSPF network types and neighbor state progression; a common trap is assuming 2WAY is always an error, when it is actually expected on multi-access segments unless the link is point-to-point. Remember the memory tip: “DR and BDR go FULL, DROTHERs stay 2WAY.”
300-410 Device Access Control Practice Question
This 300-410 practice question tests your understanding of device access control. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A network engineer runs the following command on Router R1:
R1# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
192.168.1.2 1 FULL/DR 00:00:35 10.1.1.2 GigabitEthernet0/0
192.168.2.2 1 2WAY/DROTHER 00:00:32 10.2.2.2 GigabitEthernet0/1
192.168.3.2 1 FULL/BDR 00:00:38 10.3.3.2 GigabitEthernet0/2
The neighbor on Gi0/1 is not forming a full adjacency because it is in 2WAY state.
In OSPF, the 2WAY state indicates that the router has received a Hello from the neighbor but has not yet exchanged database descriptors; a FULL state is required for complete adjacency.
B
The neighbor on Gi0/0 is the DR, which is causing high CPU usage.
Why wrong: Being the DR is normal and does not necessarily indicate high CPU usage.
C
The neighbor on Gi0/2 is the BDR, which is a problem because it should be the DR.
Why wrong: BDR is a normal role in OSPF multi-access networks.
D
All neighbors are in FULL state, indicating no issues.
Why wrong: The neighbor on Gi0/1 is in 2WAY, not FULL, so there is an issue.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The neighbor on Gi0/1 is not forming a full adjacency because it is in 2WAY state.
The neighbor on Gi0/1 is in the 2WAY/DROTHER state, which is normal for non-DR/BDR routers on a multi-access network; however, the question implies a potential issue because the engineer might expect all neighbors to reach FULL state. In OSPF, the 2WAY state is a valid adjacency state for DROTHER routers, but if the network is a point-to-point link or the engineer expects full connectivity, this state indicates that the neighbor is not exchanging LSAs (Link State Advertisements) with this router, which could be a problem if the link is not a broadcast multi-access network. The 2WAY state is formed after the two-way communication is established, but it does not progress to FULL unless the router is the DR or BDR, so this is not necessarily an error, but it is the only state that is not FULL, making it the potential issue highlighted in the question.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 neighbor on Gi0/1 is not forming a full adjacency because it is in 2WAY state.
Why this is correct
In OSPF, the 2WAY state indicates that the router has received a Hello from the neighbor but has not yet exchanged database descriptors; a FULL state is required for complete adjacency.
Related concept
Read the scenario before looking for a memorised answer.
✗
The neighbor on Gi0/0 is the DR, which is causing high CPU usage.
Why it's wrong here
Being the DR is normal and does not necessarily indicate high CPU usage.
✗
The neighbor on Gi0/2 is the BDR, which is a problem because it should be the DR.
Why it's wrong here
BDR is a normal role in OSPF multi-access networks.
✗
All neighbors are in FULL state, indicating no issues.
Why it's wrong here
The neighbor on Gi0/1 is in 2WAY, not FULL, so there is an issue.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that any state other than FULL indicates a problem, but in OSPF multi-access networks, the 2WAY state between DROTHER routers is normal and expected, so candidates must recognize that the 'issue' is context-dependent and that the output shows a valid adjacency state for a non-DR/BDR router.
Detailed technical explanation
How to think about this question
In OSPF broadcast multi-access networks, only the DR and BDR form FULL adjacencies with all other routers on the segment; DROTHER routers only exchange LSAs with the DR and BDR, resulting in a 2WAY state between DROTHER routers. This behavior is defined in RFC 2328, Section 9.3, and is designed to reduce the number of adjacencies and LSA flooding overhead. A common real-world scenario is when an engineer misconfigures an interface as broadcast on a point-to-point link, causing unexpected 2WAY states and incomplete routing information exchange.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Device Access Control — This question tests Device Access Control — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The neighbor on Gi0/1 is not forming a full adjacency because it is in 2WAY state. — The neighbor on Gi0/1 is in the 2WAY/DROTHER state, which is normal for non-DR/BDR routers on a multi-access network; however, the question implies a potential issue because the engineer might expect all neighbors to reach FULL state. In OSPF, the 2WAY state is a valid adjacency state for DROTHER routers, but if the network is a point-to-point link or the engineer expects full connectivity, this state indicates that the neighbor is not exchanging LSAs (Link State Advertisements) with this router, which could be a problem if the link is not a broadcast multi-access network. The 2WAY state is formed after the two-way communication is established, but it does not progress to FULL unless the router is the DR or BDR, so this is not necessarily an error, but it is the only state that is not FULL, making it the potential issue highlighted in the question.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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