Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
Exhibit
R1# interface GigabitEthernet0/0 ipv6 address fe80::1 link-local ipv6 ospf 10 area 0 ! ipv6 router ospf 10 router-id 1.1.1.1 R2# interface GigabitEthernet0/0 ipv6 address fe80::2 link-local ipv6 ospf 10 area 1 ! ipv6 router ospf 10 router-id 2.2.2.2
Two directly connected routers running OSPFv3 do not form an adjacency. Both interfaces have valid IPv6 addresses and can ping each other using link-local addresses. Based on the exhibit, what is the most likely cause?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Best answer
The interfaces are assigned to different OSPFv3 areas.
This is correct because OSPFv3 neighbors on the same link must agree on the area.
B
Distractor review
The routers need global unicast addresses before OSPFv3 can run.
This is wrong because OSPFv3 can form neighbor relationships using link-local communication on the link.
C
Distractor review
The router IDs must be identical before adjacency can form.
This is wrong because router IDs must be unique, not identical.
D
Distractor review
The link-local addresses must be learned from DHCPv6.
This is wrong because link-local addresses do not require DHCPv6 in this way.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is to assume that because two routers can ping each other using IPv6 link-local addresses, their OSPFv3 adjacency should automatically form. This mistake overlooks the critical requirement that both routers must be configured in the same OSPFv3 area. Candidates might also incorrectly believe that global unicast addresses are necessary for OSPFv3 adjacency or that router IDs must be identical. These misconceptions lead to selecting incorrect answers, as adjacency depends on matching area IDs and unique router IDs, not on global addressing or identical IDs.
Technical deep dive
How to think about this question
OSPFv3 is the version of the OSPF routing protocol designed to support IPv6 networks. It uses IPv6 link-local addresses for neighbor discovery and adjacency formation, which means routers communicate directly over the local link without requiring global unicast addresses. The core concept is that OSPFv3 neighbors must be configured in the same OSPF area to exchange routing information and form adjacencies. This area consistency ensures that routers share a common routing domain and can synchronize their link-state databases. The decision process for OSPFv3 adjacency formation involves several checks: routers must be directly connected, have matching area IDs on their interfaces, agree on interface types, and have compatible authentication settings if enabled. Even if routers can ping each other using link-local addresses, a mismatch in the OSPF area configuration prevents adjacency formation. This is because OSPF treats area ID as a fundamental parameter for neighbor relationships, and any discrepancy causes the routers to reject adjacency. A common exam trap is assuming that successful IPv6 ping between routers guarantees OSPFv3 adjacency. While link-local ping confirms Layer 3 reachability, OSPFv3 adjacency depends on protocol-level parameters matching exactly. Another practical behavior is that router IDs must be unique but not identical; identical router IDs cause adjacency failure but are not a prerequisite for adjacency. Understanding these nuances helps avoid misconfiguration and troubleshooting errors in IPv6 OSPF deployments.
KKey Concepts to Remember
- OSPFv3 requires all routers on a common link to be configured in the same OSPF area to successfully form neighbor adjacencies.
- OSPFv3 uses IPv6 link-local addresses for neighbor discovery and adjacency formation, so global unicast addresses are not mandatory for adjacency.
- Each OSPF router must have a unique router ID; identical router IDs prevent adjacency formation but are not required to be the same.
- Link-local addresses in IPv6 are automatically configured and do not require DHCPv6 for OSPFv3 neighbor communication.
- OSPFv3 adjacency formation depends on matching protocol parameters such as area ID, interface type, and authentication settings.
- Successful IPv6 ping using link-local addresses confirms basic Layer 3 connectivity but does not guarantee OSPFv3 adjacency.
- OSPFv3 adjacency failure often results from configuration mismatches rather than physical or Layer 3 connectivity issues.
- OSPFv3 maintains similar adjacency rules as OSPFv2, emphasizing the importance of consistent area configuration across neighbors.
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.
Related practice questions
Related 200-301 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
CCNA subnetting practice questions
Practise IPv4 subnetting, CIDR, masks, host ranges and subnet selection.
CCNA OSPF practice questions
Practise OSPF neighbours, router IDs, metrics, areas and routing-table interpretation.
CCNA VLAN practice questions
Practise VLANs, access ports, trunks, allowed VLANs and switching scenarios.
CCNA STP practice questions
Practise spanning tree, root bridge election, port roles and STP troubleshooting.
CCNA EtherChannel practice questions
Practise LACP, PAgP, port-channel behaviour and bundle requirements.
CCNA ACL practice questions
Practise standard and extended ACLs, permit/deny logic and traffic filtering.
CCNA NAT practice questions
Practise static NAT, dynamic NAT, PAT and inside/outside address translation.
CCNA DHCP practice questions
Practise DHCP scopes, relay, leases and troubleshooting.
CCNA show ip route practice questions
Practise routing-table output, longest-prefix match, AD and route selection.
CCNA show interfaces trunk practice questions
Practise trunk verification and VLAN forwarding across switches.
CCNA wireless security practice questions
Practise WLAN security, authentication and wireless architecture concepts.
CCNA IPv6 practice questions
Practise IPv6 addressing, routes, neighbour discovery and common IPv6 exam traps.
More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?
Question 2
A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?
Question 3
What is the OSPF metric called?
Question 4
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Question 5
A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?
Question 6
A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?
FAQ
Questions learners often ask
What does this 200-301 question test?
OSPFv3 requires all routers on a common link to be configured in the same OSPF area to successfully form neighbor adjacencies.
What is the correct answer to this question?
The correct answer is: The interfaces are assigned to different OSPFv3 areas. — The most likely cause is an OSPFv3 area mismatch on the interface. In practical terms, OSPFv3 still requires neighbors on the same link to agree on the area assignment, just as OSPF for IPv4 does. Link-local reachability alone is not enough to form an adjacency. The protocol parameters still have to match. This is an important IPv6 routing point because people sometimes assume that successful IPv6 ping means the routing protocol should automatically work. It does not. Adjacency depends on protocol alignment, not just basic connectivity.
What should I do if I get this 200-301 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
Discussion
Loading comments…
Sign in to join the discussion.