OSPF neighbour adjacencies, route advertisements, and DR/BDR elections appear consistently on the CCNA. These questions test whether you can read OSPF state from show commands and identify why two routers fail to reach FULL adjacency or why a route isn't being learned.
Start Scenario PracticeA 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?
Explanation: 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.
Two routers are directly connected over IPv6 and should form an OSPFv3 adjacency, but they do not. Link-local addressing is present on both interfaces. Which issue is most likely to prevent the adjacency?
Explanation: An area mismatch is a strong and direct explanation. In plain language, even though the routers can have valid IPv6 addressing and proper link-local communication on the interface, OSPFv3 still requires the two ends of the shared segment to agree on the area context for the adjacency. If one side places the interface in one area and the other side places it in another, the routers will not treat each other as valid neighbors. This is very similar in principle to OSPF for IPv4. Link-local addressing matters in OSPFv3, but the protocol still enforces key neighbor-formation checks. The correct answer is the one that focuses on a required protocol match rather than on a vague issue like hostname or cable color.
R1 and R2 are directly connected. Both are configured in OSPF area 0, and they can successfully ping each other. However, OSPF neighbor adjacency fails. R1's interface is configured with `ip ospf authentication message-digest` and a valid key, while R2's interface has no OSPF authentication configured. What is the most likely cause?
Explanation: The most likely cause is an OSPF authentication mismatch. Although the routers have IP connectivity and are in the same OSPF area, OSPF adjacency requires matching security parameters. R1 uses message-digest authentication whereas R2 has none configured, preventing neighbor formation. The other options are incorrect: the stem confirms they are in the same area (A), OSPF does not require identical hostnames (C), and successful pings prove the subnet mask does not block multicast traffic (D).
R1 learns the route 192.0.2.0/24 via OSPF, RIP, and a static route configured with an administrative distance of 130. Based on this information, which two statements are correct?
Explanation: The router installs the OSPF route because it has the lowest administrative distance among the routes shown. The static route with AD 130 is intentionally floating, and the RIP route has a higher AD than OSPF. Route selection first prefers longest match, then lower AD among routes to the same prefix length.
A junior network engineer configured a floating static route on Router R1 to provide backup connectivity to a remote network 10.10.10.0/24. The primary connection uses OSPF. However, after the primary link fails, hosts on R1 cannot reach the remote network. The OSPF adjacency is down, and the floating static route is not appearing in the routing table. Based on the exhibit, what is the most likely cause of the issue?
Explanation: Option B is correct because the floating static route's next-hop becomes unreachable after the primary OSPF link fails. In the exhibit, the next-hop IP is likely configured to an address that is only reachable via OSPF; when that adjacency drops, the router has no route to the next-hop, so it cannot recursively resolve the static route. As a result, the route does not appear in the routing table. Option A is wrong because the route is present in the configuration (as a floating static route). Option C is wrong because the administrative distance of the floating static route is intentionally higher than OSPF's so that it only installs when OSPF fails; this is correct behavior. Option D is wrong because a default route would not override a more specific static route to 10.10.10.0/24.
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Practice all OSPF Troubleshooting ScenariosOSPF neighbour adjacencies, route advertisements, and DR/BDR elections appear consistently on the CCNA. These questions test whether you can read OSPF state from show commands and identify why two routers fail to reach FULL adjacency or why a route isn't being learned. These appear throughout the 200-301 and require you to apply your knowledge, not just recall facts.
Cisco doesn't publish an exact breakdown, but scenario-based questions (especially exhibit and command-output formats) make up a significant portion of the 200-301. Practicing each scenario type ensures you're ready for any format.
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