The answer is that the interface GigabitEthernet0/0 is missing the `ospfv3 1 ipv6 area 0` command. This is correct because OSPFv3, unlike OSPFv2, does not automatically enable on an interface when the OSPF process is started globally; it requires an explicit interface-level configuration to begin sending Hello packets and forming adjacencies. Without this command, the interface remains passive to OSPFv3, so no neighbor relationship can establish. On the CCNA 200-301 v2 exam, this question tests your understanding of the fundamental OSPFv3 interface configuration requirement, often tripping up candidates who assume OSPFv3 behaves identically to OSPFv2. A common trap is thinking the global `ipv6 router ospf 1` command alone is sufficient, but the interface must be explicitly tied to an area. Remember the memory tip: "No interface command, no Hello packets"—if you don't see neighbors, always check that the interface has the `ospfv3 [process-id] ipv6 area [area-id]` command applied.
CCNA IP Routing Practice Question
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.
Exhibit
R1# show ospfv3 neighbor
OSPFv3 1 address-family ipv6 (router-id 1.1.1.1)
Neighbor ID Pri State Dead Time Interface ID Interface
R1# show ipv6 interface brief
GigabitEthernet0/0 [up/up]
FE80::1
GigabitEthernet0/1 [up/up]
FE80::2
R1# show running-config | section router ospfv3
router ospfv3 1
address-family ipv6
router-id 1.1.1.1
area 0
interface GigabitEthernet0/0
interface GigabitEthernet0/1
R1# show running-config interface GigabitEthernet0/0
interface GigabitEthernet0/0
ipv6 address FE80::1 link-local
ipv6 ospfv3 1 ipv6 area 0
!
A network engineer is troubleshooting OSPFv3 adjacency between two directly connected Cisco routers, R1 and R2, both running IOS-XE. The engineer configures OSPFv3 on both routers but notices that the adjacency does not form. The engineer runs 'show ospfv3 neighbor' on R1 and sees no neighbors. What is the most likely cause of this issue?
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.
R1# show ospfv3 neighbor
OSPFv3 1 address-family ipv6 (router-id 1.1.1.1)
Neighbor ID Pri State Dead Time Interface ID Interface
R1# show ipv6 interface brief
GigabitEthernet0/0 [up/up]
FE80::1
GigabitEthernet0/1 [up/up]
FE80::2
R1# show running-config | section router ospfv3
router ospfv3 1
address-family ipv6
router-id 1.1.1.1
area 0
interface GigabitEthernet0/0
interface GigabitEthernet0/1
R1# show running-config interface GigabitEthernet0/0
interface GigabitEthernet0/0
ipv6 address FE80::1 link-local
ipv6 ospfv3 1 ipv6 area 0
!
A
The OSPFv3 process ID must match on both routers.
Why wrong: OSPFv3 process IDs are locally significant and do not need to match for adjacency to form.
B
The interface GigabitEthernet0/0 is missing the 'ospfv3 1 ipv6 area 0' command.
Without this command, OSPFv3 is not enabled on the interface, preventing adjacency formation.
C
The link-local addresses are not in the same subnet.
Why wrong: Link-local addresses are only used for neighbor discovery and do not require subnet matching; they are always on the same link.
D
The router ID 1.1.1.1 is duplicated on R2.
Why wrong: Duplicate router IDs can cause issues, but the 'show ospfv3 neighbor' output would typically show the neighbor in EXSTART or EXCHANGE state, not missing entirely.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The interface GigabitEthernet0/0 is missing the 'ospfv3 1 ipv6 area 0' command.
Option B is correct because OSPFv3 requires explicit interface-level configuration to enable the protocol on a specific interface. The correct command is 'ospfv3 1 ipv6 area 0' (or 'ipv6 ospf 1 area 0' for the traditional OSPFv3 configuration). Without this command, the interface does not participate in OSPFv3, so no Hello packets are sent or received, preventing adjacency formation.
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.
✗
The OSPFv3 process ID must match on both routers.
Why it's wrong here
OSPFv3 process IDs are locally significant and do not need to match for adjacency to form.
✓
The interface GigabitEthernet0/0 is missing the 'ospfv3 1 ipv6 area 0' command.
Why this is correct
Without this command, OSPFv3 is not enabled on the interface, preventing adjacency formation.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The link-local addresses are not in the same subnet.
Why it's wrong here
Link-local addresses are only used for neighbor discovery and do not require subnet matching; they are always on the same link.
✗
The router ID 1.1.1.1 is duplicated on R2.
Why it's wrong here
Duplicate router IDs can cause issues, but the 'show ospfv3 neighbor' output would typically show the neighbor in EXSTART or EXCHANGE state, not missing entirely.
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.
✓The interface GigabitEthernet0/0 is missing the 'ospfv3 1 ipv6 area 0' command.Correct answer▾
Why this is correct
Without this command, OSPFv3 is not enabled on the interface, preventing adjacency formation.
✗The OSPFv3 process ID must match on both routers.Wrong answer — click to see why▾
Why this is wrong here
This is a common misconception; OSPFv3 uses the router ID for neighbor identification, not the process ID.
✗The link-local addresses are not in the same subnet.Wrong answer — click to see why▾
Why this is wrong here
Link-local addresses are automatically configured and do not affect OSPFv3 adjacency as long as they are unique.
✗The router ID 1.1.1.1 is duplicated on R2.Wrong answer — click to see why▾
Why this is wrong here
In this scenario, no neighbors are seen, indicating a more fundamental issue like OSPFv3 not being enabled on the interface.
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: answer the scenario, not the keyword
Cisco often tests the distinction between OSPFv2 (where enabling the protocol under the routing process automatically activates it on all interfaces with 'network' statements) and OSPFv3 (which requires explicit per-interface activation), leading candidates to overlook the mandatory interface-level command.
Trap categories for this question
Command / output trap
Duplicate router IDs can cause issues, but the 'show ospfv3 neighbor' output would typically show the neighbor in EXSTART or EXCHANGE state, not missing entirely.
Detailed technical explanation
How to think about this question
OSPFv3 (RFC 5340) fundamentally differs from OSPFv2 in that it runs per-link rather than per-subnet, using link-local addresses for all OSPF packet exchanges. The 'ipv6 ospfv3' command under the interface is mandatory because OSPFv3 does not automatically enable on all IPv6-enabled interfaces; this design prevents unintended routing protocol overhead. In real-world deployments, forgetting this command is a common misconfiguration when migrating from OSPFv2.
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 200-301 question in full detail.
IP Routing — This question tests IP Routing — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The interface GigabitEthernet0/0 is missing the 'ospfv3 1 ipv6 area 0' command. — Option B is correct because OSPFv3 requires explicit interface-level configuration to enable the protocol on a specific interface. The correct command is 'ospfv3 1 ipv6 area 0' (or 'ipv6 ospf 1 area 0' for the traditional OSPFv3 configuration). Without this command, the interface does not participate in OSPFv3, so no Hello packets are sent or received, preventing adjacency formation.
What should I do if I get this 200-301 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". 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.
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