ANS-C01 Network Design Practice Question
A company has a Direct Connect connection with a private VIF to a VPC. They want to add a second Direct Connect connection for redundancy. Both connections will terminate at the same Direct Connect gateway. Which TWO steps are required to enable BGP multipath (ECMP) across the two connections?
⚠ Common exam trap
AWS often tests the misconception that using different ASNs or different prefixes is required for redundancy, but the key to ECMP is identical ASN and identical prefixes to enable equal-cost multipath routing.
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
✓
Ensure the same customer-side ASN is used on both virtual interfaces.
To enable BGP multipath (ECMP) across two Direct Connect connections terminating on the same Direct Connect gateway, you must use the same customer-side ASN on both virtual interfaces. This allows the Direct Connect gateway to treat both paths as equal-cost routes. Additionally, you must advertise the same BGP prefixes on both virtual interfaces so that the gateway sees identical routes from both paths and can load-balance traffic across them.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Ensure the same customer-side ASN is used on both virtual interfaces.
Why this is correct
Same ASN is required for ECMP.
- ✗
Use a different autonomous system number (ASN) on each virtual interface.
Why it's wrong here
Different ASNs would break ECMP.
- ✗
Advertise different BGP prefixes on each virtual interface.
Why it's wrong here
Different prefixes would not be equal cost.
- ✓
Advertise the same BGP prefixes (routes) on both virtual interfaces.
Why this is correct
Same prefixes are needed for ECMP.
- ✗
Attach each virtual interface to a different VPC.
Why it's wrong here
ECMP requires same VPC target.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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