CCNA IP Routing Practice Question
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?
⚠ Common exam trap
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.
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
✓
The interface GigabitEthernet0/0 is missing the 'ospfv3 1 ipv6 area 0' command.
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.
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 only meaningful on the local router and do not influence the OSPFv3 neighbor relationship. Each router can run a different process ID number as long as the interface has been enabled for OSPFv3 in the same IPv6 area. Neighborship depends on stable parameters such as area ID, hello/dead timers, and MTU, not on the process ID. Therefore, a mismatch would not prevent R1 from seeing R2 in the neighbor table.
- ✓
The interface GigabitEthernet0/0 is missing the 'ospfv3 1 ipv6 area 0' command.
Why this is correct
With OSPFv3, enabling the OSPF process globally is not enough; each participating interface must be explicitly activated with the 'ospfv3 1 ipv6 area 0' interface-level configuration. This command assigns the interface to the OSPFv3 process 1 for address family IPv6 and places it into area 0. Without this command, the router will not send or listen for OSPFv3 Hello messages on GigabitEthernet0/0, so no neighbor adjacency can ever form. That is exactly why R2's neighbor entry is missing from the 'show ospfv3 neighbor' output.
- ✗
The link-local addresses are not in the same subnet.
Why it's wrong here
ICMPv6 and OSPFv3 use link-local addresses (fe80::/10) exclusively for neighbor discovery and for exchange of routing information on the local segment. These addresses are only required to be unique on the link, never globally or in the same subnet as the remote peer. Because both interfaces are on the same Ethernet segment, their link-local addresses are automatically valid for OSPFv3 communication. A subnet mismatch of link-local addresses is therefore impossible and cannot be the cause of a missing neighbor entry.
- ✗
The router ID 1.1.1.1 is duplicated on R2.
Why it's wrong here
If the router ID 1.1.1.1 were actually duplicated, the routers would still discover each other via Hello packets and move through OSPF state machine into EXSTART/EXCHANGE before the duplicate ID is detected and the adjacency is halted. The absence of any neighbor entry at all, rather than a stuck state, indicates that OSPFv3 packets are not being processed on the interface. Duplicate router IDs are also unlikely in this scenario because the question only shows a missing neighbor on R1, not a conflict log. So this is not the correct explanation.
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
With OSPFv3, enabling the OSPF process globally is not enough; each participating interface must be explicitly activated with the 'ospfv3 1 ipv6 area 0' interface-level configuration. This command assigns the interface to the OSPFv3 process 1 for address family IPv6 and places it into area 0. Without this command, the router will not send or listen for OSPFv3 Hello messages on GigabitEthernet0/0, so no neighbor adjacency can ever form. That is exactly why R2's neighbor entry is missing from the 'show ospfv3 neighbor' output.
✗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?”
Visual reference
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
Go deeper
Related to this question
Learn chapter
OSPFv3 Single-Area Configuration for IPv6
Key term
IPv6
IPv6 is the most recent version of the Internet Protocol, designed to replace IPv4 by providing a vastly larger number of unique addresses and improved network features.
Key term
Area 0
Area 0 is the backbone area in OSPF routing that connects all other OSPF areas to ensure a loop-free and efficient network routing topology.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 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 200-301 exam.