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200-901 Practice Question: Is designing a data center network with…
A network engineer is designing a data center network with leaf-spine topology. The requirement is to minimize latency and maximize bandwidth for east-west traffic. Which type of links should be used between leaf and spine switches?
⚠ Common exam trap
Cisco often tests the misconception that link aggregation (LACP or VSS) is the best way to increase bandwidth in a leaf-spine design, but the trap is that these are Layer 2 solutions that do not provide the active-active multipath routing (ECMP) required for optimal east-west traffic in a Layer 3 leaf-spine topology.
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
✓
Multiple parallel links with ECMP routing
In a leaf-spine topology, east-west traffic (server-to-server) must traverse the spine switches. Using multiple parallel links with Equal-Cost Multi-Path (ECMP) routing allows all links to be active simultaneously, maximizing bandwidth and minimizing latency by load-balancing traffic across all available paths. ECMP leverages Layer 3 routing (e.g., OSPF or BGP) to forward packets over multiple equal-cost paths, which is ideal for the non-blocking, high-throughput design of leaf-spine architectures.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Multiple links with VSS
Why it's wrong here
VSS is proprietary and not standard for leaf-spine.
- ✗
Single link with LACP
Why it's wrong here
LACP bundles ports but still single logical link.
- ✓
Multiple parallel links with ECMP routing
Why this is correct
ECMP allows all links to be active, increasing bandwidth and reducing latency.
- ✗
Single link with STP
Why it's wrong here
STP blocks redundant links, reducing bandwidth.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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