The answer is a mismatched OSPFv3 network type on the serial link, such as point-to-multipoint, which prevents the adjacency from progressing past INIT. On point-to-point serial interfaces, OSPFv3 defaults to the point-to-point network type, which uses link-local addresses for neighbor discovery and expects a direct two-way handshake. If one router is configured with a non-default network type like point-to-multipoint, it will not send the correct Database Description packets or may require a designated router election, causing the receiving router to see Hello packets but remain stuck in INIT. This scenario tests your understanding of OSPFv3 adjacency mechanics and network type behavior, a common trap on the Cisco CCNP ENARSI 300-410 exam where engineers overlook that serial links are not always point-to-point by default. A quick memory tip: if you see INIT but hear Hellos, check the network type—point-to-point needs no DR, so any other type breaks the handshake.
300-410 IPv6 First Hop Security Practice Question
This 300-410 practice question tests your understanding of ipv6 first hop security. 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.
A network engineer is troubleshooting IPv6 routing issues between two routers connected via a serial link. Router R1 and Router R2 are running OSPFv3. The OSPFv3 adjacency is not forming. Router R1 has the following relevant configuration:
interface Serial0/0
ipv6 address 2001:DB8:1::1/64
ipv6 ospf 1 area 0
!
Router R2 shows: debug ipv6 ospf hello output indicates that R2 is receiving Hello packets from R1, but the neighbor state remains INIT. 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 serial interface has a mismatched network type, such as point-to-multipoint, which prevents adjacency formation on a point-to-point link.
On point-to-point serial links, OSPFv3 uses link-local addresses for neighbor discovery. If the link-local address is not properly formed or if there is a mismatch in the OSPFv3 network type, the adjacency may not progress. The correct answer identifies that the serial interface is configured with a non-default network type (e.g., point-to-multipoint) that requires additional configuration, causing the INIT state to persist.
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.
✗
The OSPFv3 process ID does not match between R1 and R2.
Why it's wrong here
OSPFv3 process IDs are locally significant; they do not need to match.
✓
The serial interface has a mismatched network type, such as point-to-multipoint, which prevents adjacency formation on a point-to-point link.
Why this is correct
A network type mismatch can cause Hello packets to be ignored or not processed correctly, leading to INIT state.
The IPv6 address on the serial interface is not in the same subnet as R2's address.
Why it's wrong here
Serial links typically use link-local addresses; global addresses are not required for adjacency.
✗
The OSPFv3 hello interval is set to a non-default value that is not supported on serial links.
Why it's wrong here
Hello intervals can be adjusted; the issue is more fundamental.
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.
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 300-410 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 300-410 OSPF questions on adjacency and route selection.
IPv6 First Hop Security — This question tests IPv6 First Hop Security — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The serial interface has a mismatched network type, such as point-to-multipoint, which prevents adjacency formation on a point-to-point link. — On point-to-point serial links, OSPFv3 uses link-local addresses for neighbor discovery. If the link-local address is not properly formed or if there is a mismatch in the OSPFv3 network type, the adjacency may not progress. The correct answer identifies that the serial interface is configured with a non-default network type (e.g., point-to-multipoint) that requires additional configuration, causing the INIT state to persist.
What should I do if I get this 300-410 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 300-410 OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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 300-410 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 300-410 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.