This 200-301 practice question tests your understanding of ip routing. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. 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.
Network Topology
You are connected to R1 via the console. Configure OSPFv2 on R1 and R2 to establish a single-area OSPF adjacency in area 0. The link between R1 (G0/0) and R2 (G0/0) uses 10.0.0.0/30, and both routers must use an MTU of 1500. The current configuration has mismatched hello/dead timers and an area mismatch, preventing adjacency. Fix all issues so that R1 and R2 become fully adjacent.
R1#show running-config | section router ospf
router ospf 1
router-id 1.1.1.1
network 10.0.0.0 0.0.0.3 area 1
!
interface GigabitEthernet0/0
ip address 10.0.0.1 255.255.255.252
ip ospf hello-interval 10
ip ospf dead-interval 40
mtu 1500
!
R2#show running-config | section router ospf
router ospf 1
router-id 2.2.2.2
network 10.0.0.0 0.0.0.3 area 0
!
interface GigabitEthernet0/0
ip address 10.0.0.2 255.255.255.252
ip ospf hello-interval 5
ip ospf dead-interval 20
mtu 1500
!
A
On R1, change the network statement to area 0 and set the hello interval to 5 under interface G0/0.
This corrects both mismatches: the area mismatch (R1 was in area 1, R2 in area 0) and the hello/dead timer mismatch (R1 had 10/40, R2 had 5/20). Setting hello to 5 automatically adjusts dead to 20, matching R2.
B
On R2, change the network statement to area 1 and set the hello interval to 10 under interface G0/0.
Why wrong: This is incorrect because it changes R2 to area 1, but the question specifies area 0. Also, R2's timers would become 10/40, which would not match R1's original timers (10/40) but the goal is to match the correct timers as per the scenario.
C
On R1, change the network statement to area 0 and set the MTU to 1500 under interface G0/0.
Why wrong: This is incorrect because the MTU is already 1500 on both sides (as stated in the question). The issue is the hello/dead timers, not MTU. Changing MTU is unnecessary and does not fix the timer mismatch.
D
On R2, change the network statement to area 0 and set the dead interval to 40 under interface G0/0.
Why wrong: This is incorrect because R2 already has area 0 correct. Changing the dead interval to 40 would create a mismatch (R2 would have hello 5/dead 40, while R1 has hello 10/dead 40). The dead interval must be four times the hello interval; setting dead to 40 without changing hello to 10 would break the ratio.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
On R1, change the network statement to area 0 and set the hello interval to 5 under interface G0/0.
The adjacency fails because of two mismatches: the OSPF area on R1 is area 1 while R2 uses area 0, and the hello/dead timers differ (R1: 10/40, R2: 5/20). To fix, on R1 change the network statement to area 0 and adjust the hello interval to 5 (which also automatically sets dead to 20). Option B is wrong because it places the adjacency in area 1 (not area 0) and does not fix the timer mismatch on R2. Option C is wrong because it does not address the hello/dead timer mismatch; the MTU is already correct at 1500. Option D is wrong because it leaves the hello interval mismatched (10 vs 5) and alters the dead interval unnecessarily; the dead interval is automatically derived from the hello interval.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
On R1, change the network statement to area 0 and set the hello interval to 5 under interface G0/0.
Why this is correct
This corrects both mismatches: the area mismatch (R1 was in area 1, R2 in area 0) and the hello/dead timer mismatch (R1 had 10/40, R2 had 5/20). Setting hello to 5 automatically adjusts dead to 20, matching R2.
On R2, change the network statement to area 1 and set the hello interval to 10 under interface G0/0.
Why it's wrong here
This is incorrect because it changes R2 to area 1, but the question specifies area 0. Also, R2's timers would become 10/40, which would not match R1's original timers (10/40) but the goal is to match the correct timers as per the scenario.
✗
On R1, change the network statement to area 0 and set the MTU to 1500 under interface G0/0.
Why it's wrong here
This is incorrect because the MTU is already 1500 on both sides (as stated in the question). The issue is the hello/dead timers, not MTU. Changing MTU is unnecessary and does not fix the timer mismatch.
✗
On R2, change the network statement to area 0 and set the dead interval to 40 under interface G0/0.
Why it's wrong here
This is incorrect because R2 already has area 0 correct. Changing the dead interval to 40 would create a mismatch (R2 would have hello 5/dead 40, while R1 has hello 10/dead 40). The dead interval must be four times the hello interval; setting dead to 40 without changing hello to 10 would break the ratio.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓On R1, change the network statement to area 0 and set the hello interval to 5 under interface G0/0.Correct answer▾
Why this is correct
This corrects both mismatches: the area mismatch (R1 was in area 1, R2 in area 0) and the hello/dead timer mismatch (R1 had 10/40, R2 had 5/20). Setting hello to 5 automatically adjusts dead to 20, matching R2.
✗On R2, change the network statement to area 1 and set the hello interval to 10 under interface G0/0.Wrong answer — click to see why▾
Why this is wrong here
The area should be 0, not 1. Changing R2 to area 1 would still leave an area mismatch if R1 is changed to area 0, and the timer change is unnecessary.
Why candidates choose this
Candidates might think they can adjust either router to match, but the question implies fixing R1 to match R2's correct settings.
✗On R1, change the network statement to area 0 and set the MTU to 1500 under interface G0/0.Wrong answer — click to see why▾
Why this is wrong here
The MTU is already correct; the problem is timer and area mismatch. Adjusting MTU does not affect OSPF adjacency if timers are mismatched.
Why candidates choose this
Candidates may think MTU mismatch is a common OSPF issue, but here it is explicitly stated as matching. They might focus on MTU instead of timers.
✗On R2, change the network statement to area 0 and set the dead interval to 40 under interface G0/0.Wrong answer — click to see why▾
Why this is wrong here
R2's area is already correct; the dead interval should be 20 to match hello 5. Setting dead to 40 would cause a timer mismatch.
Why candidates choose this
Candidates might think adjusting the dead interval alone can fix the mismatch, but OSPF requires both hello and dead intervals to match, and the dead interval must be consistent with the hello interval.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Trap categories for this question
Scenario analysis trap
This is incorrect because it changes R2 to area 1, but the question specifies area 0. Also, R2's timers would become 10/40, which would not match R1's original timers (10/40) but the goal is to match the correct timers as per the scenario.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.
TExam Day Tips
→Check area mismatch first when OSPF adjacency fails.
→Review passive interfaces when a network is advertised but no neighbour forms.
→Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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 neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 200-301 OSPF questions on adjacency and route selection.
IP Routing — This question tests IP Routing — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: On R1, change the network statement to area 0 and set the hello interval to 5 under interface G0/0. — The adjacency fails because of two mismatches: the OSPF area on R1 is area 1 while R2 uses area 0, and the hello/dead timers differ (R1: 10/40, R2: 5/20). To fix, on R1 change the network statement to area 0 and adjust the hello interval to 5 (which also automatically sets dead to 20). Option B is wrong because it places the adjacency in area 1 (not area 0) and does not fix the timer mismatch on R2. Option C is wrong because it does not address the hello/dead timer mismatch; the MTU is already correct at 1500. Option D is wrong because it leaves the hello interval mismatched (10 vs 5) and alters the dead interval unnecessarily; the dead interval is automatically derived from the hello interval.
What should I do if I get this 200-301 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 200-301 OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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