The correct choice is to implement a leaf-spine topology with multiple spine switches and ECMP. This design meets high availability and east-west traffic requirements because multiple spine switches eliminate any single point of failure, while Equal-Cost Multi-Path (ECMP) routing enables load balancing across all available spine links, ensuring that any leaf can reach any other leaf in a single hop with maximum bandwidth utilization. On the ENCOR 350-401 exam, this concept tests your understanding of modern data center architectures and how ECMP supports non-blocking, scalable east-west flows—a common trap is assuming that a single spine pair or traditional three-tier design can provide the same redundancy and consistent latency. Remember the memory tip: "More spines, more wins with ECMP" to recall that multiple spine switches paired with ECMP are essential for both high availability and efficient east-west traffic.
CCNP Network Function Virtualization Practice Question
This 350-401 practice question tests your understanding of network function virtualization. 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 enterprise is migrating its data center to a leaf-spine architecture. The design must provide high availability and support for east-west traffic patterns. Which design choice best meets these requirements?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Implement a leaf-spine topology with multiple spine switches and ECMP.
A leaf-spine topology with multiple spine switches and Equal-Cost Multi-Path (ECMP) routing provides high availability by eliminating single points of failure and supports east-west traffic patterns by ensuring that any leaf switch can reach any other leaf switch with a consistent number of hops (typically one hop via a spine). ECMP allows load balancing across all available spine links, maximizing bandwidth and redundancy for data center east-west flows.
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.
✗
Deploy a collapsed core with a single pair of core switches.
Why it's wrong here
Collapsed core may create bottlenecks for east-west traffic and lacks the scalability of leaf-spine.
✗
Use a three-tier hierarchical design with access, distribution, and core layers.
Why it's wrong here
Traditional three-tier is optimized for north-south traffic, not east-west.
✓
Implement a leaf-spine topology with multiple spine switches and ECMP.
Why this is correct
Leaf-spine with ECMP provides high bandwidth, low latency, and redundancy for east-west traffic.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use a ring topology connecting all switches in a loop.
Why it's wrong here
Ring topologies are not suitable for data center east-west traffic due to limited bandwidth and convergence issues.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that a three-tier design is always more reliable or that a collapsed core is sufficient for modern data centers, but the trap here is that candidates overlook the specific requirement for east-west traffic patterns, which demands a flat, non-blocking fabric like leaf-spine with ECMP rather than traditional hierarchical or ring topologies.
Detailed technical explanation
How to think about this question
In a leaf-spine architecture, each leaf switch connects to every spine switch, forming a full mesh. ECMP (often using OSPF or BGP with equal-cost routes) allows traffic to be distributed across multiple spine links based on flow hashing (e.g., using source/destination IP or L4 ports). Under the hood, the spine switches act as a non-blocking fabric, and the number of spine switches can be scaled independently of leaf switches, enabling linear bandwidth expansion. A real-world scenario is a large-scale virtualization cluster where VM-to-VM traffic (east-west) must traverse minimal hops to reduce latency and jitter; leaf-spine with ECMP achieves this by keeping all paths at two hops maximum.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network Function Virtualization — This question tests Network Function Virtualization — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Implement a leaf-spine topology with multiple spine switches and ECMP. — A leaf-spine topology with multiple spine switches and Equal-Cost Multi-Path (ECMP) routing provides high availability by eliminating single points of failure and supports east-west traffic patterns by ensuring that any leaf switch can reach any other leaf switch with a consistent number of hops (typically one hop via a spine). ECMP allows load balancing across all available spine links, maximizing bandwidth and redundancy for data center east-west flows.
What should I do if I get this 350-401 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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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