mediumMultiple Choice
350-401 Practice Question: A campus network architect is redesigning the LAN…
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?
⚠ Common exam trap
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.
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.
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
A collapsed core design collapses the core and distribution layers into one, but the access layer remains, so east-west traffic must still traverse two or more switch hops. Redundant core switches only provide failover; they do not eliminate the oversubscription at the access-to-core uplinks or the added latency of moving traffic through multiple ASIC layers. This architecture lacks the non-blocking, uniform path characteristics of a leaf-spine fabric.
- ✓
Leaf-spine design with all leaf switches connected to all spine switches.
Why this is correct
A leaf-spine design connects every leaf switch to every spine switch, creating a full-mesh fabric at the spine layer while keeping each leaf's uplinks identical. Every server-to-server flow takes at most two hops, and with ECMP (Equal-Cost Multipathing), traffic is spread across all spines, avoiding oversubscription and providing predictable, low latency. Scaling is horizontal — adding another spine increases bandwidth and path options without rewiring existing leaves.
- ✗
Mesh design where every switch connects to every other switch.
Why it's wrong here
A full mesh where every switch connects to every other switch creates a direct path for every pair but requires n*(n-1)/2 physical links. For 10 switches that is 45 links, and for 50 switches it becomes 1,225 links — an exponential increase in cabling, ports, and administrative overhead that makes the design impractical beyond a few devices. It also provides no benefit over leaf-spine for east-west traffic because leaf-spine already gives two-hop paths with fewer, more manageable connections.
- ✗
Traditional three-tier design with access, distribution, and core layers.
Why it's wrong here
A traditional three-tier design separates access, distribution, and core layers, forcing all inter-VLAN or server-to-server traffic to travel up the distribution layer and through the core before returning. Each hop introduces switching latency and consumes bandwidth on the uplinks, and the core becomes a central bottleneck for east-west traffic. Unlike leaf-spine, where every path is identical and predictable, three-tier has varied path lengths, making latency and capacity harder to guarantee.
Go deeper
Related to this question
Learn chapter
Spine-Leaf and Software-Defined Network Architectures
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
Two-Tier vs Three-Tier Architecture
Two-Tier and Three-Tier Architecture are network design models that separate network functions into layers to improve performance, security, and manageability, with the two-tier model having a collapsed core and distribution layer, and the three-tier model adding a separate core layer.
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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.