The answer is the router with the highest router ID. This is correct because in an OSPF multi-access network, the Designated Router (DR) election first compares OSPF priority values; when all interfaces share the default priority of 1, the tie is broken by selecting the router with the highest Router ID. The Router ID is typically the highest loopback or physical IP address on the router, and this mechanism ensures a deterministic DR is chosen to manage LSA flooding and reduce adjacency overhead. On the CompTIA Network+ N10-009 exam, this concept tests your understanding of OSPF election logic, and a common trap is assuming the highest IP address on the segment itself determines the DR—it is actually the Router ID, not the interface IP. A helpful memory tip: think of the DR election as a two-step ladder—priority first, then Router ID as the tiebreaker, so when priorities are equal, the “biggest ID” wins.
N10-009 Network Implementation Practice Question
This N10-009 practice question tests your understanding of network implementation. 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.
An OSPF network uses a multi-access segment with four routers. All router interfaces have the default OSPF priority of 1. Which router becomes the Designated Router (DR)?
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 router ID
In an OSPF multi-access network, the Designated Router (DR) is elected based on the highest OSPF priority value, with a tie-breaking mechanism using the highest Router ID. Since all routers have the default priority of 1, the router with the highest Router ID wins the DR election. This ensures a stable topology for reducing LSA flooding and adjacency overhead.
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 router ID
Why this is correct
Correct. When priorities are equal, the highest router ID determines the DR.
Related concept
Read the scenario before looking for a memorised answer.
✗
The router with the lowest IP address on the segment
Why it's wrong here
The election uses router ID, not the lowest IP on the segment.
✗
The router with the highest bandwidth on the connecting interface
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the DR election tie-breaker with the OSPF route selection metric (cost/bandwidth) or assume the lowest IP address is used, but the actual tie-breaker is the highest Router ID after priority.
Detailed technical explanation
How to think about this question
The DR election process is defined in RFC 2328, where each router sends Hello packets containing its priority and Router ID. The Router ID is typically the highest loopback IP address or the highest physical interface IP address, and it is used as the final tie-breaker when priorities are equal. In a real-world scenario, if an administrator wants a specific router to be the DR, they manually set its OSPF priority to a higher value (e.g., 255) to override the default election.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this N10-009 question in full detail.
Network Implementation — This question tests Network Implementation — 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 router ID — In an OSPF multi-access network, the Designated Router (DR) is elected based on the highest OSPF priority value, with a tie-breaking mechanism using the highest Router ID. Since all routers have the default priority of 1, the router with the highest Router ID wins the DR election. This ensures a stable topology for reducing LSA flooding and adjacency overhead.
What should I do if I get this N10-009 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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Question Discussion
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