Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
Exhibit
R1# show ip ospf interface g0/0 GigabitEthernet0/0 is up, line protocol is up Internet Address 10.1.12.1/30, Area 0 Network Type POINT_TO_POINT R2# show ip ospf interface g0/0 GigabitEthernet0/0 is up, line protocol is up Internet Address 10.1.12.2/30, Area 0 Network Type BROADCAST
A router pair is directly connected, but they do not become OSPF neighbors. IP addressing and area assignment are correct. Based on the output, what is the most likely cause?
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
Best answer
OSPF network type mismatch on the connected interfaces
This is correct because one side is using point-to-point and the other is using broadcast, which can prevent a stable adjacency.
B
Distractor review
Duplicate default routes on both routers
This is wrong because the issue described is neighbor formation, not route selection involving default routes.
C
Distractor review
Missing VLAN trunking on the link
This is wrong because the interfaces shown are routed OSPF interfaces, not switch trunks.
D
Distractor review
The OSPF process IDs are required to match
This is wrong because OSPF process IDs are locally significant.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is assuming that OSPF process IDs must match on both routers to form neighbors. Many candidates mistakenly believe process IDs are globally significant, but they are only locally important identifiers. Another tempting mistake is blaming IP addressing or area mismatches without checking the OSPF network type. Since network type controls how OSPF hellos are sent and received, a mismatch between broadcast and point-to-point types can silently block adjacency formation even when IP and area configurations appear correct. This subtlety often leads to confusion during troubleshooting and exam scenarios.
Technical deep dive
How to think about this question
OSPF (Open Shortest Path First) is a link-state routing protocol that forms neighbor adjacencies between routers on directly connected networks. One critical parameter for adjacency formation is the OSPF network type configured on the interfaces. Network types define how OSPF treats the link, such as broadcast, point-to-point, point-to-multipoint, or non-broadcast multi-access (NBMA). These types influence the hello and dead intervals, DR/BDR election, and neighbor discovery mechanisms. For two routers to become OSPF neighbors, their network types on the connected interfaces must match. If one router treats the link as broadcast (expecting DR/BDR elections and multicast hellos) and the other treats it as point-to-point (no DR/BDR, unicast hellos), the hello packets and neighbor expectations will not align, preventing adjacency formation. This mismatch causes the routers to see each other but never establish full neighbor states despite correct IP addressing and area assignments. This scenario is a common CCNA exam trap because candidates often verify IP addressing and area IDs but overlook network type consistency. Practically, mismatched network types cause OSPF adjacency failures even when physical connectivity is perfect. Cisco IOS allows manual configuration of network types, so understanding this behavior helps troubleshoot adjacency issues in lab and production environments.
KKey Concepts to Remember
- OSPF requires matching network types on connected interfaces to successfully form neighbor adjacencies and exchange routing information.
- The OSPF network type determines hello packet behavior, DR/BDR election, and neighbor discovery mechanisms on a link.
- A mismatch between broadcast and point-to-point network types prevents OSPF routers from establishing stable adjacencies despite correct IP and area settings.
- OSPF process IDs are locally significant and do not need to match for neighbor relationships to form.
- Duplicate default routes do not affect OSPF neighbor formation but influence routing decisions after adjacency is established.
- VLAN trunking is irrelevant for routed OSPF interfaces because OSPF operates at Layer 3, not Layer 2 switching.
- OSPF adjacency failures due to network type mismatches often show interfaces up and in the same subnet but no neighbor state progression.
- Correctly configuring OSPF network types ensures consistent hello intervals and neighbor expectations, enabling adjacency formation.
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 requires matching network types on connected interfaces to successfully form neighbor adjacencies and exchange routing information.
What is the correct answer to this question?
The correct answer is: OSPF network type mismatch on the connected interfaces — The most likely cause is an OSPF network type mismatch. In plain language, the routers are connected and trying to run OSPF, but they do not agree on how the link should behave from OSPF’s perspective. OSPF expects several adjacency-related parameters to align, and network type is one of them. If one side treats the segment as point-to-point and the other treats it as broadcast, the hello process and neighbor expectations do not line up cleanly. This is a classic CCNA troubleshooting pattern because the obvious items such as IP addressing and area membership can still look correct. The real clue is hidden in the interface-level OSPF output. When the network type differs, adjacency formation can fail even though the interfaces are up and the routers are in the same subnet. That makes the network-type mismatch the most defensible answer.
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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