350-601 Network Practice Question
In a spine-leaf architecture using eBGP, which of the following is the recommended BGP configuration for the spine switches?
⚠ Common exam trap
Cisco often tests the misconception that all spine switches should share a single ASN for simplicity, but the trap here is that this breaks eBGP’s loop prevention and prevents ECMP load balancing across spines.
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
✓
Unique ASN for each spine switch
In eBGP-based spine-leaf architectures, each spine switch should use a unique ASN to enable BGP’s loop prevention mechanism (the AS_PATH attribute). This ensures that leaf switches can detect and discard routes received from two different spines that originated from the same leaf, preventing routing loops and allowing load balancing across multiple spines. A unique ASN per spine is the recommended design per Cisco’s best practices for data center fabrics.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
No BGP; use OSPF instead
Why it's wrong here
eBGP is commonly used in spine-leaf for scalability and control.
- ✗
Single ASN for all spines
Why it's wrong here
Using a single ASN would cause BGP to see the spine as a single hop, reducing path diversity.
- ✓
Unique ASN for each spine switch
Why this is correct
Each spine gets a unique ASN so that leaves see multiple AS paths, enabling ECMP.
- ✗
Same ASN as leaves
Why it's wrong here
Leaves and spines should be in different ASNs to maintain eBGP peering.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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