Question 130 of 2,015

OSPF →mediumDrag & DropObjective-mapped

Quick Answer

The answer is "Build routing table from shortest-path tree" as the final step. This is correct because the Dijkstra algorithm, which OSPF uses for SPF calculation, systematically constructs a loop-free shortest-path tree by first initializing a candidate list with the root router, then repeatedly moving the lowest-cost candidate into the tree database and updating neighbor path costs, and only after the entire tree is built does it derive the routing table entries from that tree. On the ENCOR 350-401 exam, this drag-and-drop question tests your understanding of the sequential logic behind OSPF’s SPF process, often tripping candidates who mistakenly place the routing table build earlier or confuse it with the neighbor cost update step. A common trap is thinking the routing table is built incrementally, but Dijkstra finalizes the tree first. To remember the order, use the mnemonic: "Initialize, Iterate, Tree, Table" — or simply "IIT-T" — where the last T always stands for the routing table built from the completed tree.

350-401 OSPF Practice Question

This 350-401 practice question tests your understanding of ospf. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

Drag and drop the steps of OSPF SPF calculation steps (Dijkstra) into the correct order, from first to last.

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.

Question 1mediumdrag order

Review the full OSPF breakdown →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

Initialize candidate list with root router

The Dijkstra algorithm first initializes the candidate list with the root node, then iteratively moves the lowest-cost candidate to the tree, updating neighbor costs, and finally builds the routing table from the shortest-path tree.

Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.

Common exam traps

Common exam trap: OSPF can fail even when IP connectivity looks correct

OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.

Detailed technical explanation

How to think about this question

OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.

KKey Concepts to Remember

OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.

TExam Day Tips

Check area mismatch first when OSPF adjacency fails.
Review passive interfaces when a network is advertised but no neighbour forms.
Use show ip ospf neighbor and show ip route clues carefully.

Key takeaway

OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.

Real-world example

How this comes up in practice

A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.

What to study next

Got this wrong? Here's your next step.

Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 350-401 OSPF questions on adjacency and route selection.

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FAQ

Questions learners often ask

What does this 350-401 question test?

OSPF — This question tests OSPF — OSPF neighbours must agree on key parameters..

What is the correct answer to this question?

The correct answer is: Initialize candidate list with root router — The Dijkstra algorithm first initializes the candidate list with the root node, then iteratively moves the lowest-cost candidate to the tree, updating neighbor costs, and finally builds the routing table from the shortest-path tree.

What should I do if I get this 350-401 question wrong?

Are there clue words in this question I should notice?

Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.

What is the key concept behind this question?

OSPF neighbours must agree on key parameters.

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Same concept, more angles

1 more ways this is tested on 350-401

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. Drag and drop the steps of OSPF SPF calculation steps (Dijkstra) into the correct order, from first to last.

medium

✓ A.Initialize candidate list with root router
✓ B.Examine root's neighbors and add to candidate list
✓ C.Move lowest-cost candidate to SPF tree
✓ D.Examine new router's neighbors and update candidate list
✓ E.Terminate when all routers in SPF tree

Why A: The Dijkstra SPF algorithm first initializes the candidate list with the root router itself. It then examines the root's neighbors, adding them to the candidate list. The router with the lowest cost is moved from candidate to the SPF tree. The process repeats by examining the newly added router's neighbors and updating the candidate list. Finally, when all routers are in the SPF tree, the algorithm terminates and the routing table is populated.

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