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 PracticeRefer to the exhibit. R1 has two equal-cost OSPF E2 routes to 10.1.1.0/24 via two different next hops. However, when tracing to 10.1.1.1, all traffic uses the path through 10.0.1.2. What is the most likely reason?
Explanation: OSPF E2 routes do not include the internal cost to the ASBR; the cost shown in the routing table is the external metric only. When two E2 routes have the same external metric, Cisco IOS uses the interface cost as a tie-breaker to select the best next hop. In this scenario, the interface to 10.0.1.2 has a lower cost than the interface to 10.0.2.2, so all traffic is forwarded via 10.0.1.2.
Which THREE conditions are required for OSPF routers to become fully adjacent? (Choose three.)
Explanation: OSPF routers must share the same area ID to form a full adjacency because the area ID defines the link-state database scope. Routers in different areas cannot exchange Type 1 LSAs directly; they rely on ABRs for inter-area routing. Without matching area IDs, the routers will not even proceed to the 2-Way state.
Refer to the exhibit. An administrator needs to ensure that traffic to 192.168.1.0/24 is forwarded via a different path than traffic to 192.168.2.0/24, even though both routes are learned via OSPF with the same metric. Which action should the administrator take?
Explanation: Option B is correct because adding a static route for 192.168.1.0/24 with a lower administrative distance (e.g., 1) than OSPF (default 110) forces the router to prefer the static route over the OSPF-learned route, even though the OSPF metric is the same. This allows traffic to 192.168.1.0/24 to use a different next-hop (e.g., 10.0.0.1) while traffic to 192.168.2.0/24 continues using the OSPF-learned path via 10.0.0.2, achieving the desired path differentiation without altering OSPF metrics or using complex PBR.
A network administrator is troubleshooting an issue where OSPF routes are not being learned from a neighbor. The administrator checks the OSPF configuration and sees that both routers are in the same area. The neighbor state is stuck in EXSTART. What is the most likely cause?
Explanation: When OSPF neighbors are stuck in the EXSTART state, it typically indicates a problem with the Database Description (DBD) packet exchange process. The most common cause is an MTU mismatch between the interfaces, because OSPF will not proceed to the Exchange state if the DBD packet is larger than the interface MTU and gets silently dropped. This prevents the routers from agreeing on the master/slave relationship and exchanging link-state information.
Examine the following configuration snippet: interface GigabitEthernet0/1 ip address 192.168.1.1 255.255.255.0 ip ospf hello-interval 20 ip ospf dead-interval 80 What is the effect of this configuration?
Explanation: Option A is correct because the configuration explicitly sets the OSPF hello interval to 20 seconds and the dead interval to 80 seconds, which maintains the default 4:1 ratio (dead = hello × 4). OSPF allows manual configuration of these timers, and as long as both sides of the adjacency match, the ratio can be any value; the 4:1 default is not enforced by the protocol.
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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 350-401 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 350-401. Practicing each scenario type ensures you're ready for any format.
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