Question 1,722 of 1,819
IP RoutingmediumMultiple SelectObjective-mapped

OSPF DR/BDR Election Rules

This 200-301 practice question tests your understanding of ip routing. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.

Which TWO statements correctly describe OSPFv2 DR/BDR election behavior in a multi-access network?

Quick Answer

The answer is that the router with the highest OSPF interface priority is elected as the Designated Router (DR), and if priorities are equal, the router with the highest Router ID (RID) wins the election. This is because OSPFv2 DR/BDR election rules on a multi-access network first compare the configured priority value (0-255), where a higher number is preferred, and only fall back to the RID as a tiebreaker. On the CCNA 200-301 v2 exam, this topic tests your understanding of Layer 3 redundancy and adjacency formation, often appearing in a scenario where you must identify which router becomes DR after a link failure. A common trap is forgetting that a priority of 0 means the router will never be elected, and that the election is non-preemptive—a higher-priority router added later will not take over until the current DR fails. For a quick memory tip, remember "P-RID": Priority first, then Router ID, and if you see a zero, that router is a zero-chance candidate.

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

The router with the highest OSPF interface priority is elected as the DR.

Options A and C are correct: OSPFv2 DR election first compares interface priority (highest wins), and if equal, the highest Router ID (RID) wins. Option B is incorrect because a priority of 0 prevents a router from ever becoming DR or BDR. Option D is incorrect because the election is non‑preemptive; a router with higher priority won't take over until the current DR/BDR fails. Option E is incorrect because DR and BDR form full adjacencies with all routers on the segment, not just with each other.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • The router with the highest OSPF interface priority is elected as the DR.

    Why this is correct

    The DR is elected based on the highest interface priority (0-255, default 1).

    Related concept

    Read the scenario before looking for a memorised answer.

  • A router with OSPF priority 0 can become the BDR if no other router has a higher priority.

    Why it's wrong here

    A priority of 0 means the router is ineligible for election as DR or BDR.

  • If two routers have equal priority, the router with the highest router ID (RID) is elected as the DR.

    Why this is correct

    When priorities are equal, the highest RID (usually the highest loopback or interface IP) determines the DR.

    Related concept

    Read the scenario before looking for a memorised answer.

  • The DR election is preemptive; a new router with a higher priority will immediately take over as DR.

    Why it's wrong here

    OSPF DR/BDR election is not preemptive; once elected, the DR and BDR remain until failure.

  • All routers on a multi-access network form full adjacencies with the DR and BDR only.

    Why it's wrong here

    DROTHER routers form full adjacencies only with the DR and BDR, not with each other (they stay in 2-way state).

Option-by-option analysis

Why each answer is right or wrong

Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.

The router with the highest OSPF interface priority is elected as the DR.Correct answer

Why this is correct

The DR is elected based on the highest interface priority (0-255, default 1).

A router with OSPF priority 0 can become the BDR if no other router has a higher priority.Wrong answer — click to see why

Why this is wrong here

Priority 0 excludes the router from DR/BDR election entirely; it can only become a DROTHER.

The DR election is preemptive; a new router with a higher priority will immediately take over as DR.Wrong answer — click to see why

Why this is wrong here

A new router with a higher priority does not trigger a new election unless the existing DR or BDR goes down.

All routers on a multi-access network form full adjacencies with the DR and BDR only.Wrong answer — click to see why

Why this is wrong here

DROTHERs do not form full adjacencies among themselves; they only exchange LSAs via the DR/BDR.

Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”

Common exam traps

Common exam trap: answer the scenario, not the keyword

Cisco often tests the misconception that a priority 0 router can become BDR if no other router has a higher priority, but in reality, priority 0 means the router is never elected as DR or BDR.

Detailed technical explanation

How to think about this question

The DR/BDR election is non-preemptive; once elected, they remain until failure or OSPF process restart, even if a higher-priority router joins later. The router ID is typically the highest loopback IP or active interface IP, and priority values range from 0 to 255, with 1 being the default. In real-world designs, setting priority to 0 on spoke routers in a hub-and-spoke topology prevents them from becoming DR/BDR, reducing unnecessary LSA flooding.

KKey Concepts to Remember

  • Read the scenario before looking for a memorised answer.
  • Find the constraint that changes the correct option.
  • Eliminate answers that are true in general but not in this case.

TExam Day Tips

  • Watch for words such as best, first, most likely and least administrative effort.
  • Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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.

Quick reference

Routing Protocol Comparison

ProtocolMetricMax HopsAlgorithmType
RIP v2Hop count15Bellman-FordDistance vector
OSPFCost (bandwidth)UnlimitedDijkstra (SPF)Link state
EIGRPComposite metricUnlimitedDUALHybrid
IS-ISCostUnlimitedDijkstraLink state
BGPPolicy / attributesUnlimitedPath vectorPath vector

RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.

What to study next

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FAQ

Questions learners often ask

What does this 200-301 question test?

IP Routing — This question tests IP Routing — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The router with the highest OSPF interface priority is elected as the DR. — Options A and C are correct: OSPFv2 DR election first compares interface priority (highest wins), and if equal, the highest Router ID (RID) wins. Option B is incorrect because a priority of 0 prevents a router from ever becoming DR or BDR. Option D is incorrect because the election is non‑preemptive; a router with higher priority won't take over until the current DR/BDR fails. Option E is incorrect because DR and BDR form full adjacencies with all routers on the segment, not just with each other.

What should I do if I get this 200-301 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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Last reviewed: Jun 11, 2026

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