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350-401 Practice Question: Deploying a new data center and needs to choose…
A company is deploying a new data center and needs to choose between a three-tier (core, aggregation, access) and a spine-leaf architecture. The network engineer is concerned about east-west traffic patterns for server virtualization. Which architecture is most suitable and why?
⚠ Common exam trap
Cisco often tests the misconception that three-tier architecture is more redundant or easier to manage, but the key trap here is that candidates may overlook how east-west traffic patterns require non-blocking, low-latency paths that only a spine-leaf design with ECMP can provide.
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
✓
Spine-leaf, because it provides equal-cost multipath (ECMP) for all leaf-to-leaf traffic.
Spine-leaf architecture is most suitable for east-west traffic patterns because it provides a full mesh of connections between leaf switches and spine switches, enabling equal-cost multipath (ECMP) routing. This allows all leaf-to-leaf traffic to traverse multiple parallel paths with equal cost, maximizing bandwidth utilization and minimizing latency, which is critical for server virtualization traffic that often moves between hypervisors.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Spine-leaf, because it provides equal-cost multipath (ECMP) for all leaf-to-leaf traffic.
Why this is correct
Spine-leaf is correct because it structurally guarantees equal-cost multipath (ECMP) between any pair of leaf switches: every leaf is exactly one hop from every spine, so all available spine-to-spine links are equally weighted. This allows flow-level load balancing across all spine links simultaneously, maximizing bisectional bandwidth for east-west traffic. Unlike three-tier designs that rely on spanning-tree-computed forwarding paths, spine-leaf leverages Layer 3 ECMP, which also ensures consistent low latency and no idle redundancy links.
- ✗
Three-tier, because it offers more redundancy with multiple aggregation layers.
Why it's wrong here
The three-tier design does not actually offer better redundancy; it simply adds more devices and layers. More aggregation layers create a larger Layer 2 domain where spanning tree must block redundant paths to prevent loops, meaning many of those 'extra' links are unusable for forwarding. Even when multiple active paths exist at the core, north-south traffic is concentrated through the aggregation layer, creating a bottleneck. Redundancy in a spine-leaf design is inherently better because every leaf has multiple active path to every spine, and failures are handled by ECMP re-routing rather than by STP reconvergence.
- ✗
Spine-leaf, because it supports legacy spanning tree protocols.
Why it's wrong here
Spine-leaf architectures specifically avoid legacy spanning tree protocols to achieve their performance benefits. Spine-leaf is designed as a routed fabric, commonly using BGP or OSPF at Layer 3, which enables ECMP and eliminates STP's blocked ports and slow convergence. If legacy STP were applied, it would disable redundant spine links and destroy the equal-cost forwarding that makes spine-leaf attractive. Thus, supporting legacy STP is not a benefit but would be a regression to the same limitations that spine-leaf is meant to overcome.
- ✗
Three-tier, because it is easier to manage with traditional VLANs.
Why it's wrong here
While traditional VLANs may seem simpler for VLAN-based segmentation, this ease of management is not the primary design criterion for an enterprise data center network. Three-tier networks often carry VLANs across the entire Layer 2 domain, which can cause stability issues and require spanning-tree tuning. Spine-leaf can also support VLANs, typically using VXLAN to overlay Layer 2 over a Layer 3 fabric, preserving operational familiarity while providing much better east-west throughput. Therefore, familiarity with traditional VLANs does not outweigh the fundamental architectural advantages of spine-leaf for modern traffic patterns.
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Related to this question
Learn chapter
Network Access Control and AAA
Key term
Spine-Leaf Architecture
Spine-Leaf architecture is a network topology where every lower-layer switch (leaf) connects to every upper-layer switch (spine) to provide predictable and scalable east-west traffic flow.
Key term
Fabric Fundamentals
Fabric Fundamentals is the set of core concepts behind a network fabric, where switches and routers form a single logical system that simplifies traffic forwarding and automation.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-401 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-401 exam.