The answer is EIGRP, the Enhanced Interior Gateway Routing Protocol. This is the correct choice because EIGRP is a hybrid routing protocol that combines the best features of distance-vector and link-state protocols, using the Diffusing Update Algorithm (DUAL) to achieve fast convergence by instantly calculating backup routes. It fully supports Variable-Length Subnet Masking (VLSM) through classless routing, and its default composite metric is based on bandwidth and delay, meeting the exact requirements of the scenario. On the CompTIA Network+ N10-009 exam, this question tests your ability to distinguish between dynamic routing protocols, with a common trap being to select OSPF (which also supports VLSM but uses cost as a metric) or RIPv2 (which supports VLSM but converges slowly and uses hop count). A helpful memory tip: EIGRP’s metric is often remembered as “Bandwidth and Delay” because these are the two default components in its composite formula, making it the go-to protocol when speed and path quality matter most.
N10-009 Network Implementation Practice Question
This N10-009 practice question tests your understanding of network implementation. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
A network administrator is configuring dynamic routing between two routers in the same organization. The routers must support VLSM, converge quickly, and use a metric that is based on bandwidth and delay. Which routing protocol should be configured?
Why wrong: RIP uses hop count as its metric and is classful by default; it does not support VLSM well and converges slowly.
B
OSPF
Why wrong: OSPF supports VLSM and converges quickly, but its metric is cost (based on bandwidth), not a combination of bandwidth and delay.
C
EIGRP
EIGRP is a Cisco proprietary protocol that supports VLSM, converges quickly, and uses bandwidth and delay as the default metric components.
D
BGP
Why wrong: BGP is designed for routing between autonomous systems, not for internal routing within a single organization. It uses path attributes rather than bandwidth/delay.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
EIGRP
C is correct because EIGRP is a Cisco-proprietary hybrid routing protocol that supports Variable-Length Subnet Masking (VLSM), converges rapidly using the Diffusing Update Algorithm (DUAL), and uses a composite metric that by default includes bandwidth and delay. This makes it ideal for the scenario where both VLSM support and fast convergence are required with a metric based on bandwidth and delay.
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.
✗
RIP
Why it's wrong here
RIP uses hop count as its metric and is classful by default; it does not support VLSM well and converges slowly.
✗
OSPF
Why it's wrong here
OSPF supports VLSM and converges quickly, but its metric is cost (based on bandwidth), not a combination of bandwidth and delay.
✓
EIGRP
Why this is correct
EIGRP is a Cisco proprietary protocol that supports VLSM, converges quickly, and uses bandwidth and delay as the default metric components.
Related concept
Read the scenario before looking for a memorised answer.
✗
BGP
Why it's wrong here
BGP is designed for routing between autonomous systems, not for internal routing within a single organization. It uses path attributes rather than bandwidth/delay.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose OSPF because it is a widely used link-state protocol that supports VLSM and converges quickly, but they overlook the specific requirement for a metric based on both bandwidth and delay, which is unique to EIGRP's default composite metric.
Detailed technical explanation
How to think about this question
EIGRP's composite metric is calculated using the formula: metric = [K1 * bandwidth + (K2 * bandwidth) / (256 - load) + K3 * delay] * [K5 / (reliability + K4)], with default K values (K1=1, K3=1, others=0) making it effectively bandwidth + delay. The DUAL algorithm provides loop-free fast convergence by maintaining feasible successors and performing local computations when the successor fails, avoiding the need for full route recalculation like OSPF's SPF. In real-world networks, EIGRP is often preferred for Cisco-only environments due to its lower CPU overhead and faster convergence compared to OSPF.
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: EIGRP — C is correct because EIGRP is a Cisco-proprietary hybrid routing protocol that supports Variable-Length Subnet Masking (VLSM), converges rapidly using the Diffusing Update Algorithm (DUAL), and uses a composite metric that by default includes bandwidth and delay. This makes it ideal for the scenario where both VLSM support and fast convergence are required with a metric based on bandwidth and delay.
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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