Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
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 below is captured from R2. What is the most likely reason?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Distractor review
Authentication mismatch between R2 and 3.3.3.3
A mismatch would stop the neighbor relationship from reaching 2WAY in the first place.
B
Best answer
The 2WAY state with another DROTHER on a broadcast segment is normal
DROTHER routers do not form full adjacency with every other DROTHER.
C
Distractor review
R2 must be configured as a point-to-point network type
That is not required here and would change behavior rather than explain the current normal state.
D
Distractor review
R2 has a duplicate router ID
A duplicate router ID causes other issues and is not what this output indicates.
Common exam trap
Common exam trap: answer the scenario, not the keyword
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.
Technical deep dive
How to think about this question
Open Shortest Path First (OSPF) is a link-state routing protocol that establishes neighbor adjacencies to exchange routing information. On broadcast multi-access networks like Ethernet, OSPF elects a Designated Router (DR) and a Backup Designated Router (BDR) to reduce the number of adjacencies and minimize flooding. Routers that are neither DR nor BDR assume the DROTHER role and form full adjacencies only with the DR and BDR, not with other DROTHER routers. This behavior optimizes network efficiency and reduces unnecessary overhead on the segment. The OSPF neighbor state machine progresses through several states: Down, Init, 2-Way, ExStart, Exchange, Loading, and Full. On a broadcast segment, routers reach the 2-Way state with all neighbors but only form full adjacencies with the DR and BDR. Therefore, seeing a neighbor stuck in the 2-Way state with another DROTHER router is expected and indicates normal OSPF operation. Full adjacency is only required between DR/BDR and DROTHER routers, not between DROTHER routers themselves. A common exam trap is to misinterpret the 2-Way state with a DROTHER neighbor as a problem or misconfigure network types to force full adjacency. However, this is standard OSPF behavior on broadcast networks and not a fault. Understanding this prevents unnecessary troubleshooting and misconfiguration. In practical networks, this design reduces CPU and bandwidth usage by limiting full adjacencies to only essential routers, improving scalability and stability.
KKey Concepts to Remember
- OSPF elects a Designated Router (DR) and Backup Designated Router (BDR) on broadcast multi-access networks to reduce adjacency complexity.
- Routers in the DROTHER role form full OSPF adjacencies only with the DR and BDR, not with other DROTHER routers on the same segment.
- The OSPF neighbor state 2-Way indicates bidirectional communication but does not guarantee full adjacency with all neighbors on broadcast networks.
- Full OSPF adjacency is established between DR/BDR and DROTHER routers, while DROTHER routers remain in 2-Way state with each other.
- OSPF network types influence adjacency formation; broadcast network type automatically elects DR/BDR and manages neighbor states accordingly.
- Authentication mismatches prevent OSPF neighbors from reaching 2-Way state, so adjacency stuck at 2-Way is not caused by authentication issues.
- Duplicate router IDs cause OSPF neighbor relationship failures but do not manifest as neighbors stuck in 2-Way with DROTHER routers.
- Configuring a point-to-point network type on a broadcast segment changes adjacency behavior and is unnecessary for normal Ethernet OSPF operation.
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.
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More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?
Question 2
A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?
Question 3
What is the OSPF metric called?
Question 4
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Question 5
A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?
Question 6
A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?
FAQ
Questions learners often ask
What does this 200-301 question test?
OSPF elects a Designated Router (DR) and Backup Designated Router (BDR) on broadcast multi-access networks to reduce adjacency complexity.
What is the correct answer to this question?
The correct answer is: 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.
What should I do if I get this 200-301 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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