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 10.12.12.1/30, Area 0 Network Type POINT_TO_POINT R2# show ip ospf interface g0/0 GigabitEthernet0/0 is up, line protocol is up Internet Address 10.12.12.2/30, Area 0 Network Type BROADCAST
R1 and R2 are directly connected and both configured for OSPF area 0. The IP addresses are correct, but the routers do not become neighbors. Based on the exhibit, 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
The OSPF network types on the interfaces do not match.
This is correct because OSPF network type mismatch can prevent normal adjacency formation.
B
Distractor review
The routers need matching hostnames to exchange LSAs.
This is wrong because hostnames do not determine OSPF neighbor relationships.
C
Distractor review
The /30 subnet is too small for OSPF to operate.
This is wrong because OSPF works normally over /30 point-to-point links.
D
Distractor review
The interfaces must be converted into switch trunks.
This is wrong because OSPF commonly runs over routed interfaces, not trunk ports.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is to overlook the importance of matching OSPF network types on connected interfaces. Candidates might assume that correct IP addressing and area numbers are sufficient for adjacency. However, if one router uses a broadcast network type and the other uses point-to-point, they will not become neighbors despite appearing correctly configured. This subtle mismatch is often missed because it does not generate explicit errors, leading to confusion and incorrect troubleshooting steps.
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 shared networks. One critical factor in adjacency formation is the OSPF network type configured on each interface. Common OSPF network types include broadcast, point-to-point, point-to-multipoint, and non-broadcast multi-access (NBMA). These types influence how routers discover neighbors, elect designated routers (DR/BDR), and exchange link-state advertisements (LSAs). When two routers are directly connected and configured in the same OSPF area, their interfaces must have matching OSPF network types to form a neighbor relationship. For example, if one router’s interface is set to broadcast and the other to point-to-point, the routers will not recognize each other as neighbors because their OSPF hello packets and neighbor discovery mechanisms differ. This mismatch prevents the adjacency from progressing beyond the initial state. A common exam trap is assuming that correct IP addressing and area configuration guarantee OSPF adjacency. However, the network type mismatch silently blocks adjacency formation, causing confusion. In practical networks, verifying and aligning OSPF network types on both ends of a link is essential. Cisco IOS allows explicit configuration of the OSPF network type per interface, and understanding this behavior helps troubleshoot adjacency failures effectively.
KKey Concepts to Remember
- OSPF routers must have matching network types on their directly connected interfaces to successfully form neighbor adjacencies.
- OSPF network types determine how routers discover neighbors and exchange routing information, affecting adjacency formation.
- A mismatch between broadcast and point-to-point OSPF network types prevents routers from establishing full OSPF adjacency.
- OSPF adjacency formation requires consistent area configuration and compatible interface network types on both routers.
- IP addressing correctness alone does not guarantee OSPF neighbor relationships if network types differ on interfaces.
- OSPF does not require matching hostnames for neighbor relationships; adjacency depends on interface and protocol parameters.
- OSPF operates normally over /30 subnets on point-to-point links, so subnet size is not a limiting factor for adjacency.
- OSPF runs over routed interfaces and does not require interfaces to be configured as switch trunks for adjacency.
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 routers must have matching network types on their directly connected interfaces to successfully form neighbor adjacencies.
What is the correct answer to this question?
The correct answer is: The OSPF network types on the interfaces do not match. — The most likely cause is an OSPF network type mismatch. In practical terms, both routers are on the same IP segment and both are trying to use OSPF in the same area, but they do not agree on the type of OSPF network the interface represents. That matters because OSPF behavior changes depending on the network type, including how neighbors are discovered and how adjacencies are formed. This is a classic exam-style troubleshooting case because the obvious items look correct: IP addressing works and the area matches. But a mismatch between point-to-point and broadcast expectations can still stop the relationship from forming cleanly. That makes network type mismatch the strongest answer here.
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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