Question 1hardmulti select
Full question →hardmulti selectObjective-mapped
Exhibit
R1 g0/0: area 0, ip ospf authentication message-digest R2 g0/0: area 1, no authentication
Exhibit: An OSPFv2 adjacency between two routers on Ethernet is not forming. Which two mismatches would directly prevent the routers from becoming neighbors?
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
Different OSPF area assignments on the interfaces
Neighbors on the same link must agree on the area.
B
Best answer
Authentication mismatch between the interfaces
One side expects authentication and the other does not.
C
Distractor review
Different hostnames on the routers
Hostnames do not affect OSPF adjacency.
D
Distractor review
Different loopback addresses used for management
That does not directly block the adjacency.
E
Distractor review
One router using SSH version 2
SSH settings are unrelated.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A common exam trap is selecting options like different hostnames or loopback addresses as causes for OSPF adjacency failure. Candidates may mistakenly believe that router identification parameters affect neighbor formation. However, OSPF adjacency strictly depends on protocol parameters such as area ID and authentication. Hostnames and loopback interfaces are used for management or router ID purposes but do not block adjacency. Misunderstanding this can lead to incorrect troubleshooting steps or exam answers, wasting valuable time and causing confusion.
Technical deep dive
How to think about this question
OSPFv2 (Open Shortest Path First version 2) is a link-state routing protocol widely used in IPv4 networks to dynamically exchange routing information. For OSPF routers to form an adjacency on a multi-access network like Ethernet, they must agree on several parameters, including the OSPF area ID and authentication settings. The area ID groups routers into logical segments, ensuring that routers exchange routing information only within the same area. Authentication, if configured, secures OSPF messages to prevent unauthorized routing updates. When two OSPF routers connect on an Ethernet segment, they first discover each other and then negotiate adjacency by exchanging Hello packets. If the routers have mismatched OSPF area assignments on their interfaces, they will not recognize each other as valid neighbors, preventing adjacency formation. Similarly, if one router expects authentication on the interface but the other does not provide it or uses a different authentication type or key, the Hello packets will be rejected, and adjacency will fail. These mismatches are fundamental and directly block neighbor relationships. A common exam trap is to assume that parameters like hostnames or management loopback addresses affect adjacency formation. While these are important for network management and router identification, they do not influence OSPF neighbor establishment. Another confusion arises around SSH versions or unrelated protocols, which do not impact OSPF adjacency. Understanding that OSPF adjacency depends strictly on protocol parameters like area ID and authentication avoids these pitfalls and ensures correct troubleshooting and configuration in Cisco networks.
KKey Concepts to Remember
- OSPF routers must be configured with the same area ID on interfaces to form neighbor adjacencies on a shared network segment.
- OSPF authentication settings must match exactly between routers on the same link to allow Hello packets to be accepted and adjacency to form.
- Mismatch in OSPF area assignments directly prevents routers from establishing neighbor relationships on Ethernet networks.
- Authentication mismatches cause OSPF Hello packets to be rejected, blocking adjacency formation between routers.
- Hostnames and loopback addresses do not affect OSPF adjacency formation and are irrelevant to neighbor establishment.
- SSH version differences do not impact OSPF protocol operations or adjacency formation on interfaces.
- OSPF adjacency formation requires agreement on key parameters such as area ID and authentication to exchange routing information securely.
- Understanding OSPF adjacency prerequisites helps avoid common configuration errors that prevent neighbor relationships.
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 be configured with the same area ID on interfaces to form neighbor adjacencies on a shared network segment.
What is the correct answer to this question?
The correct answer is: Different OSPF area assignments on the interfaces — On a shared OSPFv2 network, area mismatch and authentication mismatch both stop adjacency formation. Timer mismatches can also matter on some network types, but the clearest neighbor blockers in this exhibit are area and authentication.
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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