- A
Collapsed core design with redundant core switches and distribution layers.
Why wrong: Collapsed core still uses a three-tier hierarchy and can suffer from oversubscription and increased latency as traffic traverses multiple layers.
- B
Leaf-spine design with all leaf switches connected to all spine switches.
Leaf-spine provides non-blocking, low-latency paths between any two leaf switches, and scales horizontally by adding more spines.
- C
Mesh design where every switch connects to every other switch.
Why wrong: Full mesh does not scale beyond a few switches due to the exponential increase in connections and complexity.
- D
Traditional three-tier design with access, distribution, and core layers.
Why wrong: Three-tier designs have higher latency and are less efficient for east-west traffic compared to leaf-spine.
Quick Answer
The correct choice is the leaf-spine design with all leaf switches connected to all spine switches. This architecture optimizes east-west traffic by ensuring that every leaf switch is exactly one hop away from any other leaf via the spine, delivering predictable latency regardless of the traffic path. It also scales simply by adding more leaf or spine switches without reconfiguring existing links, and it uses uplinks efficiently through equal-cost multipath (ECMP) load balancing—ideal for campus LANs facing east-west traffic growth. On the ENCOR 350-401 exam, this question tests your understanding of modern data center and campus design principles, often contrasting leaf-spine with traditional three-tier or collapsed core models. A common trap is choosing a two-tier design with redundant core switches, which still introduces variable path lengths and suboptimal uplink utilization. Remember the key advantage: in a leaf-spine, every leaf is equidistant from every other leaf—think “one hop to the spine, one hop to the destination” for consistent latency.
CCNP SD-WAN Architecture Practice Question
This 350-401 practice question tests your understanding of sd-wan architecture. 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.
A campus network architect is redesigning the LAN to support high availability and east-west traffic growth. The current design uses a traditional three-tier hierarchy with a collapsed core. The architect must choose a new design that provides predictable latency, simple scalability, and efficient use of uplinks. Which design should the architect select?
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
Leaf-spine design with all leaf switches connected to all spine switches.
The leaf-spine design (option B) provides predictable latency because every leaf switch is exactly one hop away from any other leaf switch via the spine, regardless of traffic path. This design also scales simply by adding more leaf or spine switches without reconfiguring existing connections, and it uses uplinks efficiently through equal-cost multipath (ECMP) load balancing, making it ideal for east-west traffic growth in a modern data center or campus LAN.
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.
- ✗
Collapsed core design with redundant core switches and distribution layers.
Why it's wrong here
Collapsed core still uses a three-tier hierarchy and can suffer from oversubscription and increased latency as traffic traverses multiple layers.
- ✓
Leaf-spine design with all leaf switches connected to all spine switches.
Why this is correct
Leaf-spine provides non-blocking, low-latency paths between any two leaf switches, and scales horizontally by adding more spines.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Mesh design where every switch connects to every other switch.
Why it's wrong here
Full mesh does not scale beyond a few switches due to the exponential increase in connections and complexity.
- ✗
Traditional three-tier design with access, distribution, and core layers.
Why it's wrong here
Three-tier designs have higher latency and are less efficient for east-west traffic compared to leaf-spine.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that a collapsed core design is sufficient for high availability and east-west traffic, but the trap here is that candidates overlook the predictable latency and linear scalability benefits of leaf-spine, which are explicitly required by the question's criteria.
Detailed technical explanation
How to think about this question
In a leaf-spine architecture, all leaf switches connect to all spine switches, forming a Clos network that enables non-blocking, any-to-any connectivity with consistent latency. Under the hood, protocols like BGP (RFC 4271) or IS-IS are often used to advertise loopback addresses, and ECMP (Equal-Cost Multi-Path) allows traffic to be load-balanced across all available spine links, maximizing bandwidth utilization. In real-world scenarios, this design is critical for environments with high east-west traffic, such as virtual machine migrations or containerized microservices, where traditional spanning-tree-based designs would cause congestion or path blocking.
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.
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FAQ
Questions learners often ask
What does this 350-401 question test?
SD-WAN Architecture — This question tests SD-WAN Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Leaf-spine design with all leaf switches connected to all spine switches. — The leaf-spine design (option B) provides predictable latency because every leaf switch is exactly one hop away from any other leaf switch via the spine, regardless of traffic path. This design also scales simply by adding more leaf or spine switches without reconfiguring existing connections, and it uses uplinks efficiently through equal-cost multipath (ECMP) load balancing, making it ideal for east-west traffic growth in a modern data center or campus LAN.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
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Last reviewed: Jun 24, 2026
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