The answer is an area mismatch and an authentication mismatch, as these two OSPFv2 mismatches directly prevent adjacency from forming between routers on an Ethernet link. In OSPFv2, the Hello packet carries critical parameters that must match for neighbor discovery, including the area ID and authentication credentials; if either differs, the receiving router silently drops the Hello packet, blocking adjacency at the very first stage. On the CCNA 200-301 v2 exam, this concept tests your understanding of OSPF neighbor requirements versus less critical mismatches like MTU or network type, which may affect state progression but not initial adjacency. A common trap is confusing timer mismatches—while hello and dead intervals also prevent adjacency on broadcast networks, the question specifically targets the two mismatches that stop the process before any timers are even compared. Remember the mnemonic “AAA” for adjacency blockers: Area, Authentication, and (then) timers.
CCNA IP Routing Practice Question
This 200-301 practice question tests your understanding of ip routing. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: oSPF routers must be configured with the same area ID on interfaces to form neighbor adjacencies on a shared network segment.. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Different OSPF area assignments on the interfaces
On an OSPFv2 network, area mismatch and authentication mismatch both directly prevent adjacency formation. Mismatched timers (such as hello or dead intervals) also block adjacency on all network types, including Ethernet. In this scenario, the correct choices are area mismatch (A) and authentication mismatch (B).
Key principle: OSPF routers must be configured with the same area ID on interfaces to form neighbor adjacencies on a shared network segment.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Different OSPF area assignments on the interfaces
Why this is correct
Neighbors on the same link must agree on the area.
Related concept
OSPF routers must be configured with the same area ID on interfaces to form neighbor adjacencies on a shared network segment.
✓
Authentication mismatch between the interfaces
Why this is correct
One side expects authentication and the other does not.
Related concept
OSPF routers must be configured with the same area ID on interfaces to form neighbor adjacencies on a shared network segment.
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.
Detailed technical explanation
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.
Key takeaway
OSPF routers must be configured with the same area ID on interfaces to form neighbor adjacencies on a shared network segment.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Review oSPF routers must be configured with the same area ID on interfaces to form neighbor adjacencies on a shared network segment., then practise related 200-301 questions on the same topic to reinforce the concept.
IP Routing — This question tests IP Routing — 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 an OSPFv2 network, area mismatch and authentication mismatch both directly prevent adjacency formation. Mismatched timers (such as hello or dead intervals) also block adjacency on all network types, including Ethernet. In this scenario, the correct choices are area mismatch (A) and authentication mismatch (B).
What should I do if I get this 200-301 question wrong?
Review oSPF routers must be configured with the same area ID on interfaces to form neighbor adjacencies on a shared network segment., then practise related 200-301 questions on the same topic to reinforce the concept.
What is the key concept behind this question?
OSPF routers must be configured with the same area ID on interfaces to form neighbor adjacencies on a shared network segment.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This 200-301 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-301 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.