CCNA IP Routing Practice Question
Exhibit
R2#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 2.2.2.2 1 FULL/DR 00:00:33 10.1.1.2 Gig0/0 3.3.3.3 1 2WAY/DROTHER 00:00:39 10.1.1.3 Gig0/0
Exhibit: OSPF neighbors are not reaching FULL state on an Ethernet segment with multiple routers. The output of show ip ospf neighbor on R2 shows a neighbor in the 2WAY/DROTHER state. What is the most likely reason?
⚠ Common exam trap
A common exam trap is assuming that neighbors stuck in the 2-Way state indicate a problem requiring troubleshooting or configuration changes. Many candidates mistakenly believe that all OSPF neighbors on a broadcast segment must reach the FULL state with each other. However, OSPF’s design limits full adjacency to DR and BDR routers only. DROTHER routers remain in 2-Way state with each other, which is normal and expected. Misinterpreting this behavior can lead to incorrect answers such as blaming authentication or router ID issues when the output actually reflects standard OSPF operation.
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 2WAY state with another DROTHER on a broadcast segment is normal
On a broadcast Ethernet network, two routers normally become fully adjacent through the DR or BDR. If the local router is stuck in 2WAY with another DROTHER, that is normal behavior. It is not a fault by itself.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Authentication mismatch between R2 and 3.3.3.3
Why it's wrong here
An authentication mismatch between R2 and 3.3.3.3 would prevent the OSPF Hello packets from being accepted, so the neighbors would never even reach the 2WAY state. Since the exhibit shows the neighbor stuck in 2WAY, authentication has already succeeded in establishing bidirectional communication, making this option incorrect for the observed output.
When this WOULD be correct
In a different question setup where the context involves OSPF neighbors failing to establish any adjacency due to mismatched authentication settings, option A would be correct. For example, if the question described a scenario where both routers are configured with different OSPF authentication methods, this option would accurately identify the problem.
- ✓
The 2WAY state with another DROTHER on a broadcast segment is normal
Why this is correct
On a broadcast multiaccess segment, OSPF elects a DR and BDR; all other routers are DROTHERs. DROTHERs only form full adjacencies with the DR and BDR, while two DROTHERs remain in 2WAY, which is the normal and expected state. The exhibit showing R2 in 2WAY with another DROTHER is therefore not a problem, so this is the correct explanation.
- ✗
R2 must be configured as a point-to-point network type
Why it's wrong here
Changing R2 to a point-to-point network type would eliminate the DR/BDR election and force the router to form a full adjacency with the neighbor, hiding the normal 2WAY state. However, that is a configuration choice, not a requirement; the current broadcast network type is functioning correctly, and OSPF is not mandated to reach FULL with every neighbor on a broadcast segment.
When this WOULD be correct
In a different scenario where the question specifies that R2 is connected to a point-to-point link rather than a broadcast segment, configuring R2 as a point-to-point network type would be necessary to establish a full OSPF adjacency with its neighbor.
- ✗
R2 has a duplicate router ID
Why it's wrong here
A duplicate router ID would cause OSPF to reject routing information from the duplicate router, and the neighbor state would typically fluctuate or get stuck in INIT or EXSTART with error messages about duplicate router IDs. The exhibit shows a stable 2WAY state, which is not indicative of a duplicate router ID; that condition would present with much more disruptive symptoms and other output anomalies.
When this WOULD be correct
In a different scenario where the question specifies that R2 is part of an OSPF network where multiple routers have been assigned the same router ID, this option would be correct as it would directly cause OSPF to fail to establish proper neighbor relationships.
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 2WAY state with another DROTHER on a broadcast segment is normalCorrect answer▾
Why this is correct
On a broadcast multiaccess segment, OSPF elects a DR and BDR; all other routers are DROTHERs. DROTHERs only form full adjacencies with the DR and BDR, while two DROTHERs remain in 2WAY, which is the normal and expected state. The exhibit showing R2 in 2WAY with another DROTHER is therefore not a problem, so this is the correct explanation.
✗Authentication mismatch between R2 and 3.3.3.3Wrong answer — click to see why▾
Why this is wrong here
An authentication mismatch would prevent OSPF neighbors from forming any adjacency; they would not reach the 2WAY state. The output shows neighbors in 2WAY state, indicating that authentication is not the issue.
★ When this WOULD be the correct answer
In a different question setup where the context involves OSPF neighbors failing to establish any adjacency due to mismatched authentication settings, option A would be correct. For example, if the question described a scenario where both routers are configured with different OSPF authentication methods, this option would accurately identify the problem.
Why candidates choose this
Students often associate neighbor issues with authentication mismatches, but the 2WAY state proves that the routers have successfully exchanged Hello packets, which includes authentication checks.
✗R2 must be configured as a point-to-point network typeWrong answer — click to see why▾
Why this is wrong here
Configuring the interface as point-to-point would change the OSPF network type, eliminating the need for DR/BDR election and causing all routers to form full adjacencies. However, the current 2WAY state is normal for a broadcast network, so changing the network type is unnecessary and not the reason for the observed state.
★ When this WOULD be the correct answer
In a different scenario where the question specifies that R2 is connected to a point-to-point link rather than a broadcast segment, configuring R2 as a point-to-point network type would be necessary to establish a full OSPF adjacency with its neighbor.
Why candidates choose this
Students may think that changing to point-to-point solves adjacency issues, but here the 2WAY state is expected, not a problem. The point-to-point type would force full adjacencies but is not required.
✗R2 has a duplicate router IDWrong answer — click to see why▾
Why this is wrong here
A duplicate router ID would cause OSPF to reject Hello packets from the router with the duplicate ID, preventing any neighbor relationship from forming. The output shows neighbors in 2WAY state, which indicates that router IDs are unique and Hello packets are being exchanged successfully.
★ When this WOULD be the correct answer
In a different scenario where the question specifies that R2 is part of an OSPF network where multiple routers have been assigned the same router ID, this option would be correct as it would directly cause OSPF to fail to establish proper neighbor relationships.
Why candidates choose this
Duplicate router IDs are a common OSPF misconfiguration, but they would prevent the neighbor state from progressing beyond DOWN or INIT, not reach 2WAY.
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
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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
Ethernet
Ethernet is a wired networking technology that connects devices like computers, printers, and servers to each other and to the internet using cables.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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