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mediumMultiple ChoiceObjective-mapped

OSPFv3 Adjacency and Routes over IPv6 Tunnel

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?

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.

⚠ Common exam trap

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.

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 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.

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 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.

  • ✗

    The tunnel is using IPv4 transport.

    Why it's wrong here

    The output does not indicate transport; it shows OSPFv3 neighbor information.

Visual reference

R1 R2 R3 R4 10 100 10 100 OSPF picks R1→R2→R4 (cost 20) over R1→R3→R4 (cost 200)

Quick reference

Routing Protocol Comparison

ProtocolMetricMax HopsAlgorithmType
RIP v2Hop count15Bellman-FordDistance vector
OSPFCost (bandwidth)UnlimitedDijkstra (SPF)Link state
EIGRPComposite metricUnlimitedDUALHybrid
IS-ISCostUnlimitedDijkstraLink state
BGPPolicy / attributesUnlimitedPath vectorPath vector

RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.

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Same concept, more angles

1 more way this is tested on 300-410

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?

medium
  • A.The routes are learned via EIGRP.
  • B.The tunnels are using IPv4 as the transport.
  • ✓ C.OSPFv3 is running over the tunnel interfaces and these routes are reachable.
  • D.Tunnel0 has a higher metric than Tunnel1.

Why 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.

JA

Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

This 300-410 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 300-410 exam.