OSPF Adjacency State Machine Order and LSDB Synchronization
Short answer
B False, because OSPF routers synchronize the LSDB during the Exchange and Loading states before finally reaching the Full state.
Question
Key Takeaways
The main trap is reversing the cause and effect: synchronization leads to Full state, not vice versa.
This question tests your understanding of the OSPF neighbor adjacency states. The correct answer is False because LSDB synchronization happens before the Full state is reached.
Common mistake: Choosing True by assuming 'Full' means the database is fully loaded into memory without realizing it's the final step after exchange/loading.
Expert Analysis
OSPF Adjacency State Machine Sequence
The statement claims that a router enters the Full state first and then synchronizes the Link State Database (LSDB). This is incorrect because it reverses the fundamental sequence of the OSPF neighbor adjacency process. The Full state is not a prerequisite for synchronization; rather, it is the final outcome after synchronization is successfully completed.
Step-by-Step Synchronization Process
OSPF routers follow a strict order to establish adjacency:
- ExStart: Routers negotiate master/slave roles and initial sequence numbers.
- Exchange: Routers send Database Description (DBD) packets to summarize their LSDBs.
- Loading: Routers identify missing or outdated Link State Advertisements (LSAs) using LSR/LSU packets.
- Full: Once all LSDBs are synchronized and consistent, the router transitions to the Full state, indicating a complete adjacency.
Operational Consequence of Reversal
If a router were in the Full state before synchronizing, it would imply that routing decisions are being made based on incomplete topology data, leading to potential black holes or routing loops. The comments correctly note that synchronization occurs during Exchange and Loading states, with Full being the result, not the cause. Therefore, the premise that Full precedes synchronization violates OSPF protocol standards.
Exam Strategy Tip
When facing true/false questions about protocol states, always recall the chronological order: Init -> ExStart -> Exchange -> Loading -> Full. Any option suggesting a later state (like Full or 2-Way) occurs before an earlier action (like Database Exchange) is almost certainly false.
Official Reference
https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13685-3.html
This link opens the official vendor documentation in a new tab.
Exam Strategy
Memorize the OSPF state sequence as a linear timeline: Init, ExStart, Exchange, Loading, Full. If a question asks about the timing of an event relative to these states, map the event to its specific phase. For example, DBD exchange is Exchange, LSA requests are Loading, and consistency is Full. Avoid confusing the 'state name' with the 'action'; Full is a status, not an action.
Frequently Asked Questions
What happens if LSDB synchronization fails?
Can two routers be in Full state but have different LSDBs?
Community Votes
100% of anonymous learners picked answer B. Votes are pick records left by other test-takers — they are not the verified answer.
Discussion 2 contributions
Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.
From public community threads 2
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konyuz 👍 1 Answered BExstart: The routers negotiate which one will be the master and which one will be the slave for the database exchange. Exchange: The routers exchange Database Description (DBD) packets, which are summaries of their LSDBs. They use these to identify which LSAs (Link State Advertisements) they have and which ones are missing. Loading: The routers send Link State Request (LSR) packets for the missing or more recent LSAs identified during the Exchange state. The neighbor responds with Link State Update (LSU) packets containing the requested LSAs. Full: Once a router has received all the requested LSAs and its LSDB is fully synchronized with its neighbor, the neighbor relationship transitions to the Full state. Only then are they considered fully adjacent and ready to exchange routing information for path calculation.
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Fmoura17 👍 1 Answered BThe correct answer is B. False. OSPF first synchronizes the LSDB (during Exchange and Loading states), and only after synchronization is complete does it enter the Full state. Full state is the result of synchronization, not the other way around.
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