20+ practice questions focused on OSPF — one of the most tested topics on the ENCOR 350-401 exam. Each question includes a detailed explanation so you learn why the right answer is correct.
Start OSPF PracticeA network engineer is troubleshooting OSPF adjacency issues between two routers connected via a Gigabit Ethernet link. The engineer notices that the routers are stuck in the EXSTART state. Both routers have the same MTU of 1500 bytes. What is the most likely cause of this issue?
Explanation: When OSPF routers are stuck in the EXSTART state, it typically indicates a problem with the Database Description (DBD) packet exchange. Even though both routers have the same configured MTU of 1500 bytes, one router may have a lower IP MTU on its interface (e.g., due to a different interface MTU or encapsulation overhead), causing the DBD packet to be fragmented or dropped. Since OSPF DBD packets are not fragmented, a mismatch in the actual IP MTU prevents the adjacency from progressing beyond EXSTART.
An enterprise network uses OSPF as its IGP. The network engineer notices that a particular route learned via OSPF is not being installed in the routing table, even though the neighbor adjacency is up and the route appears in the OSPF database. The route is an external route redistributed from EIGRP. What is the most likely cause?
Explanation: Option C is correct because OSPF requires the forwarding address (FA) in a Type 5 LSA to be reachable via an OSPF internal route (intra-area or inter-area) for the external route to be installed in the routing table. If the FA is not reachable, the router will ignore the LSA and not install the route, even though the LSA exists in the OSPF database and the neighbor adjacency is up.
A network engineer is configuring OSPF in a multi-area design. The engineer wants to reduce the amount of LSA flooding and the size of the LSDB in area 0. Which OSPF feature should be implemented on the ABR to achieve this goal?
Explanation: Option B is correct because configuring an area filter-list on the ABR allows the engineer to filter Type 3 summary LSAs entering or leaving area 0. This directly reduces LSA flooding and shrinks the LSDB in area 0 by preventing specific inter-area prefixes from being advertised into the backbone, without altering the area type or requiring additional redistribution.
A network engineer is troubleshooting an OSPF adjacency issue between two routers connected via a serial link. The adjacency is stuck in the INIT state. The engineer has verified that the IP addresses are in the same subnet and that the link is up. What is the most likely cause?
Explanation: The INIT state in OSPF indicates that a router has received a Hello packet from its neighbor but the neighbor has not yet seen its own Router ID in the received Hello. A mismatched Hello interval causes the routers to send Hellos at different rates, so one router may not receive a Hello within the expected Dead interval, preventing the neighbor from seeing its Router ID in the received Hello and thus stalling the adjacency in INIT.
A network engineer is designing an OSPF network with multiple areas. The engineer wants to ensure that routers in area 2 can reach networks in area 0, but they should not learn any external routes from other ASs. Which OSPF area type should be configured for area 2?
Explanation: A stub area blocks Type 5 LSAs (external routes from other ASs) while allowing Type 3 summary LSAs from area 0. This ensures routers in area 2 can reach networks in area 0 via inter-area routes but do not learn external routes, meeting the requirement exactly.
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Practice all OSPF questions1. Baseline your knowledge
Start with 10 questions to gauge your current understanding of OSPF. This tells you whether you need a concept refresher or just practice.
2. Review every explanation
For each question — right or wrong — read the full explanation. Understanding why an answer is correct is more valuable than knowing the answer itself.
3. Focus on exam traps
OSPF questions on the 350-401 frequently use trap wording. Look for subtle differences in answers that test your precision, not just general knowledge.
4. Reach 80% consistently
Do repeated sessions until you score 80%+ three times in a row. Then move to mixed-mode practice to test cross-topic recall under realistic conditions.
The exact number varies per candidate. OSPF is tested as part of the ENCOR 350-401 blueprint. Practicing with targeted OSPF questions ensures you can handle any format or difficulty that appears.
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Difficulty is subjective, but OSPF is a high-priority exam concept tested in multiple ways — direct recall, scenario analysis, and command-output interpretation. Consistent practice is the best way to build confidence.
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