The answer is a missing `ipv6 ospf` interface command on one side. This is correct because the OSPFv3 `Init` state means the router has received a Hello packet from its neighbor but has not sent one back that the neighbor has received; on a point-to-point link, the most likely cause is that the interface lacks the `ipv6 ospf <process-id> area <area-id>` command, which prevents OSPFv3 from generating Hellos on that interface. For the Cisco SPCOR / CCNP Service Provider Core 350-501 exam, this question tests your ability to troubleshoot OSPFv3 interface activation in an IPv6 service provider network, and a common trap is assuming a Layer 1 or 2 issue when the real problem is a missing interface-level OSPFv3 configuration. Remember the memory tip: "Init means I hear you, but you don't hear me—check the interface for the `ipv6 ospf` command."
350-501 Networking Practice Question
This 350-501 practice question tests your understanding of networking. 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 OSPFv3 on a service provider's IPv6 network. The router shows that OSPFv3 adjacency never reaches FULL, says 'Init'. The neighbor is directly connected over a point-to-point link. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Clue: "never"
Why it matters: Absolute qualifier. True only if the statement has zero exceptions — be cautious of options that seem obvious but break down in edge cases.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Missing 'ipv6 ospf' interface command on one side
The 'Init' state in OSPFv3 indicates that the router has received a Hello packet from the neighbor but the neighbor has not received a Hello packet back. On a point-to-point link, the most common cause is that the 'ipv6 ospf <process-id> area <area-id>' interface command is missing on one side, which prevents OSPFv3 from sending Hellos on that interface. Without this command, the interface is not enabled for OSPFv3, so the neighbor never sees a Hello and the adjacency cannot progress to FULL.
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.
✗
LSA throttling prevents exchanges
Why it's wrong here
LSA throttling controls LSA generation, not adjacency formation.
✗
Mismatched OSPF router-id
Why it's wrong here
Mismatched router-id leads to adjacency failure in ExStart state.
✗
Mismatched area IDs
Why it's wrong here
Area ID mismatch causes adjacency to stall in ExStart/Exchange.
✓
Missing 'ipv6 ospf' interface command on one side
Why this is correct
OSPFv3 requires explicit interface configuration to activate adjacency.
Clue confirmation
The clue words "most likely", "never" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between OSPFv2 and OSPFv3 interface activation methods, trapping candidates who assume that OSPFv3 uses a similar 'network' command or that a global OSPF process automatically enables all interfaces.
Detailed technical explanation
How to think about this question
In OSPFv3, the 'ipv6 ospf <process-id> area <area-id>' command is required on each interface to activate OSPFv3, unlike OSPFv2 where the 'network' command under the OSPF process enables interfaces. A subtle behavior is that OSPFv3 uses link-local addresses for neighbor discovery and Hellos, so even if global IPv6 addresses are configured, the interface will not participate in OSPFv3 without this explicit command. In real-world scenarios, this often occurs when an engineer configures OSPFv3 globally but forgets to apply it to the specific interface, leading to a one-way Hello state.
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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Networking — This question tests Networking — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Missing 'ipv6 ospf' interface command on one side — The 'Init' state in OSPFv3 indicates that the router has received a Hello packet from the neighbor but the neighbor has not received a Hello packet back. On a point-to-point link, the most common cause is that the 'ipv6 ospf <process-id> area <area-id>' interface command is missing on one side, which prevents OSPFv3 from sending Hellos on that interface. Without this command, the interface is not enabled for OSPFv3, so the neighbor never sees a Hello and the adjacency cannot progress to FULL.
What should I do if I get this 350-501 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely", "never". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which THREE of the following are required for successful operation of OSPFv3 in an IPv6 service provider network?
easy
✓ A.Interface activation with 'ipv6 ospf <process> area <area>'
✓ B.OSPFv3 process configuration with router-id
✓ C.IPv6 unicast routing enabled globally
D.OSPFv3 authentication configured
E.OSPFv3 LSA type 9 for link-local addresses
Why A: Option A is correct because OSPFv3 requires interface-level activation using the 'ipv6 ospf <process> area <area>' command to enable the OSPFv3 process on a specific interface and associate it with an area. Without this, the interface will not participate in OSPFv3 neighbor discovery or routing updates, even if the process is configured globally.
Last reviewed: Jun 25, 2026
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