Quick Answer
The correct answer is that OSPFv3 adjacencies are fully established over the tunnel. This is confirmed by the FULL state shown for both neighbors in the output of the show ipv6 ospf neighbor command, which indicates that the adjacency process has completed successfully and the routers are exchanging link-state advertisements over the Tunnel0 interface. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your ability to interpret OSPFv3 neighbor states specifically over IPv6 tunnels, a common configuration for connecting disjoint IPv6 networks. A frequent trap is confusing the FULL state with a less advanced state like 2WAY or EXSTART, but remember that FULL is the final and desired adjacency state for OSPFv3. A useful memory tip: FULL means fully synchronized—both routers have identical LSDBs and are ready to route.
This 300-410 practice question tests your understanding of ipv6 tunneling techniques. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 runs the following command on Router R1:
R1# show ipv6 ospf neighbor Neighbor ID Pri State Dead Time Address Interface 192.168.1.2 1 FULL/DR 00:00:32 FE80::2 Tunnel0 192.168.1.3 1 FULL/BDR 00:00:35 FE80::3 Tunnel0
Based on this output, which statement is correct?
OSPFv3 is not running on this router.
Why wrong: Neighbors are shown, so OSPFv3 is running.
The router with Neighbor ID 192.168.1.3 is the Designated Router.
Why wrong: 192.168.1.2 is DR, 192.168.1.3 is BDR.
OSPFv3 adjacencies are fully established over the tunnel.
Both neighbors are in FULL state.
The tunnel is using IPv4 transport.
Why wrong: The output does not indicate transport; it shows OSPFv3 neighbor information.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
OSPFv3 adjacencies are fully established over the tunnel.
The output shows two OSPFv3 neighbors in the FULL state, which indicates that the adjacency process has completed successfully and the routers are exchanging link-state advertisements. The presence of the FULL state for both neighbors confirms that OSPFv3 adjacencies are fully established over the Tunnel0 interface, making option C correct.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
OSPFv3 is not running on this router.
Why it's wrong here
Neighbors are shown, so OSPFv3 is running.
The router with Neighbor ID 192.168.1.3 is the Designated Router.
Why it's wrong here
192.168.1.2 is DR, 192.168.1.3 is BDR.
OSPFv3 adjacencies are fully established over the tunnel.
Why this is correct
Both neighbors are in FULL state.
Related concept
Read the scenario before looking for a memorised answer.
The tunnel is using IPv4 transport.
Why it's wrong here
The output does not indicate transport; it shows OSPFv3 neighbor information.
Common exam traps
Cisco often tests the distinction between OSPFv2 and OSPFv3, and the trap here is that candidates may assume the presence of IPv4-like neighbor IDs (192.168.1.x) implies IPv4 transport, but OSPFv3 uses a 32-bit Router ID (often derived from an IPv4 address) regardless of the underlying IPv6 transport.
Trap categories for this question
Command / output trap
Neighbors are shown, so OSPFv3 is running.
Detailed technical explanation
OSPFv3 (OSPF for IPv6) uses link-local addresses for neighbor discovery and adjacency formation, as seen with the FE80:: addresses in the output. The FULL state indicates that the database synchronization process (exchange of DD, LSR, LSU, and LSAck packets) is complete, and the router is ready to forward traffic. In real-world scenarios, tunnels like GRE or IPv6-over-IPv4 can carry OSPFv3 traffic, but the adjacency state is independent of the underlying transport; the output here only confirms the OSPFv3 adjacency is healthy.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
IPv6 Tunneling Techniques — This question tests IPv6 Tunneling Techniques — Read the scenario before looking for a memorised answer..
The correct answer is: OSPFv3 adjacencies are fully established over the tunnel. — The output shows two OSPFv3 neighbors in the FULL state, which indicates that the adjacency process has completed successfully and the routers are exchanging link-state advertisements. The presence of the FULL state for both neighbors confirms that OSPFv3 adjacencies are fully established over the Tunnel0 interface, making option C correct.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Same concept, more angles
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. A network engineer runs the following command on Router R1: R1# show ipv6 route | include Tunnel O 2001:DB8:1::/48 [110/2] via FE80::1, Tunnel0 O 2001:DB8:2::/48 [110/3] via FE80::2, Tunnel1 Based on this output, which statement is correct?
mediumWhy C: The output shows OSPF routes (indicated by 'O') learned over tunnel interfaces. Since the routes are IPv6 (2001:DB8::/48) and OSPFv3 is the IPv6-capable version of OSPF, the correct interpretation is that OSPFv3 is running over the tunnels. The 'via FE80::1, Tunnel0' confirms the next hop is a link-local address reachable through the tunnel, meaning the routes are reachable via OSPFv3 over those tunnels.
Last reviewed: Jun 24, 2026
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