The answer is an OSPF network type mismatch, specifically because R1’s point-to-point configuration forces unicast hellos while R2’s default broadcast type expects multicast. When R1 is set to point-to-point on a multi-access link, it sends OSPF hellos directly to the neighbor’s IP address instead of the standard multicast address 224.0.0.5. R2, still using broadcast, listens only for multicast hellos, so it never receives R1’s unicast packets—leaving R2 stuck in INIT state for R1. Meanwhile, R1 receives R2’s multicast hellos and builds a full adjacency, creating the asymmetric neighbor state. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your understanding of how OSPF network type affects hello transmission and neighbor state machines; it’s a classic trap where one side shows FULL and the other INIT. Remember: point-to-point means unicast, broadcast means multicast—if they don’t match, hellos don’t cross.
300-410 IPv4 Access Control Lists Practice Question
This 300-410 practice question tests your understanding of ipv4 access control lists. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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.
OSPF is configured on a multi-access link between R1 and R2. R1 has: interface GigabitEthernet0/0, ip ospf network point-to-point. R2 has default broadcast network type. R1 shows: show ip ospf neighbor includes R2 in FULL state, but R2 shows: show ip ospf neighbor includes R1 in INIT state. What is the root cause?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The network type mismatch causes R1 to use unicast hellos, while R2 expects multicast.
When R1 is configured with 'ip ospf network point-to-point' on a multi-access link, it changes its OSPF behavior to use unicast hellos to the neighbor's IP address instead of the standard multicast address 224.0.0.5. R2, with the default broadcast network type, expects to receive OSPF hellos on the multicast address. Because R1 sends unicast hellos, R2 never receives them, so R2's neighbor state for R1 remains INIT. R1, however, receives R2's multicast hellos and can form a full adjacency from its perspective, leading to the asymmetric state.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
R1's OSPF process ID does not match R2's.
Why it's wrong here
Process ID mismatch does not affect neighbor state; area ID must match.
✓
The network type mismatch causes R1 to use unicast hellos, while R2 expects multicast.
Why this is correct
Point-to-point uses unicast; broadcast uses multicast, leading to one-way communication.
Related concept
Read the scenario before looking for a memorised answer.
Passive interface would prevent any neighbor formation.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the asymmetric neighbor state (FULL on one side, INIT on the other) as a signature symptom of OSPF network type mismatch, tempting candidates to blame mismatched process IDs or passive interfaces instead.
Detailed technical explanation
How to think about this question
In OSPF, the network type determines the hello mechanism: broadcast and non-broadcast multi-access (NBMA) use multicast (224.0.0.5) or unicast, respectively, while point-to-point uses unicast. When a mismatch occurs, the router sending unicast hellos (R1) will not be heard by the router expecting multicast (R2), but R1 can still receive R2's multicast hellos because its interface is still listening on 224.0.0.5. This creates a one-way adjacency, a classic symptom of network type mismatch. In real-world scenarios, this often happens when migrating from Frame Relay (point-to-point subinterfaces) to Ethernet without updating the OSPF network type.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 300-410 question in full detail.
IPv4 Access Control Lists — This question tests IPv4 Access Control Lists — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The network type mismatch causes R1 to use unicast hellos, while R2 expects multicast. — When R1 is configured with 'ip ospf network point-to-point' on a multi-access link, it changes its OSPF behavior to use unicast hellos to the neighbor's IP address instead of the standard multicast address 224.0.0.5. R2, with the default broadcast network type, expects to receive OSPF hellos on the multicast address. Because R1 sends unicast hellos, R2 never receives them, so R2's neighbor state for R1 remains INIT. R1, however, receives R2's multicast hellos and can form a full adjacency from its perspective, leading to the asymmetric state.
What should I do if I get this 300-410 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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