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OSPF Troubleshooting (v2/v3) →hardMultiple SelectObjective-mapped

300-410 OSPF Troubleshooting (v2/v3) Practice Question

This 300-410 practice question tests your understanding of ospf troubleshooting (v2/v3). 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.

Which TWO statements correctly describe the behavior of OSPFv3 when troubleshooting neighbor adjacency issues on a Cisco IOS-XE router? (Choose TWO.)

Question 1hardmulti select

Review the full OSPF breakdown →

A
OSPFv3 neighbor adjacencies are formed using the link-local IPv6 address of the neighbor.
Correct. OSPFv3 uses IPv6 link-local addresses for neighbor discovery and adjacency formation, not global unicast addresses.
B
The OSPFv3 router ID is a 128-bit value derived from the highest loopback IPv6 address.
Why wrong: Incorrect. The OSPFv3 router ID is still a 32-bit value, just like OSPFv2, and is typically set manually or derived from an IPv4 address.
C
The 'ipv6 router ospf' command is used to enable OSPFv3 on an interface.
Why wrong: Incorrect. The 'ipv6 router ospf' command enters OSPFv3 router configuration mode; to enable OSPFv3 on an interface, use the 'ipv6 ospf <process-id> area <area-id>' command under the interface.
D
The 'show ipv6 ospf neighbor' command displays the link-local address of each neighbor.
Correct. The 'show ipv6 ospf neighbor' command output includes the neighbor's link-local IPv6 address in the 'Address' field.
E
OSPFv3 uses the network type configured under the OSPFv3 process globally, not per interface.
Why wrong: Incorrect. The network type (e.g., broadcast, point-to-point) is configured per interface using the 'ipv6 ospf network' command, not globally.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

OSPFv3 neighbor adjacencies are formed using the link-local IPv6 address of the neighbor.

OSPFv3 uses link-local addresses for neighbor adjacency formation and relies on IPv6 link-local addresses for next-hop resolution. The router ID is still a 32-bit value, and the network type must be configured under the interface. The 'ipv6 ospf' command is used to enable OSPFv3 on an interface, not 'ipv6 router ospf'.

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.

✓
OSPFv3 neighbor adjacencies are formed using the link-local IPv6 address of the neighbor.
Why this is correct
Correct. OSPFv3 uses IPv6 link-local addresses for neighbor discovery and adjacency formation, not global unicast addresses.
Related concept
OSPF neighbours must agree on key parameters.
✗
The OSPFv3 router ID is a 128-bit value derived from the highest loopback IPv6 address.
Why it's wrong here
Incorrect. The OSPFv3 router ID is still a 32-bit value, just like OSPFv2, and is typically set manually or derived from an IPv4 address.
✗
The 'ipv6 router ospf' command is used to enable OSPFv3 on an interface.
Why it's wrong here
Incorrect. The 'ipv6 router ospf' command enters OSPFv3 router configuration mode; to enable OSPFv3 on an interface, use the 'ipv6 ospf <process-id> area <area-id>' command under the interface.
✓
The 'show ipv6 ospf neighbor' command displays the link-local address of each neighbor.
Why this is correct
Correct. The 'show ipv6 ospf neighbor' command output includes the neighbor's link-local IPv6 address in the 'Address' field.
Related concept
OSPF neighbours must agree on key parameters.
✗
OSPFv3 uses the network type configured under the OSPFv3 process globally, not per interface.
Why it's wrong here
Incorrect. The network type (e.g., broadcast, point-to-point) is configured per interface using the 'ipv6 ospf network' command, not globally.

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

Command / output trap
Incorrect. The 'ipv6 router ospf' command enters OSPFv3 router configuration mode; to enable OSPFv3 on an interface, use the 'ipv6 ospf <process-id> area <area-id>' command under the interface.

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.

What to study next

Got this wrong? Here's your next step.

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.

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FAQ

Questions learners often ask

What does this 300-410 question test?

OSPF Troubleshooting (v2/v3) — This question tests OSPF Troubleshooting (v2/v3) — OSPF neighbours must agree on key parameters..

What is the correct answer to this question?

The correct answer is: OSPFv3 neighbor adjacencies are formed using the link-local IPv6 address of the neighbor. — OSPFv3 uses link-local addresses for neighbor adjacency formation and relies on IPv6 link-local addresses for next-hop resolution. The router ID is still a 32-bit value, and the network type must be configured under the interface. The 'ipv6 ospf' command is used to enable OSPFv3 on an interface, not 'ipv6 router ospf'.

What should I do if I get this 300-410 question wrong?

What is the key concept behind this question?

OSPF neighbours must agree on key parameters.

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