ANS-C01 Network Implementation Practice Question
A company uses AWS Transit Gateway to connect multiple VPCs. The network team notices that traffic between two VPCs is taking a suboptimal path through a third VPC. What is the most likely cause?
⚠ Common exam trap
Test-takers frequently assume traffic between VPCs in a Transit Gateway always takes the most direct path, but they overlook that route table associations and propagations control the path, and a misconfigured route table can force traffic through an intermediate VPC even when a direct attachment exists.
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
✓
Incorrect route table associations and propagations in the Transit Gateway.
Incorrect route table associations and propagations in the Transit Gateway cause traffic between two VPCs to take a suboptimal path through a third VPC. The Transit Gateway uses route tables to determine the next hop for traffic; if the route table for the source VPC does not have a direct route to the destination VPC but instead has a route pointing to the third VPC (e.g., via a VPN attachment or a transit VPC attachment), traffic will be forwarded through that third VPC. This is a common misconfiguration when route propagation is not properly set up or when static routes are incorrectly prioritized.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Security groups are blocking the direct path, forcing traffic through a third VPC.
Why it's wrong here
Security groups do not influence routing decisions.
- ✗
BGP is not configured between the VPCs, so traffic defaults through a transit VPC.
Why it's wrong here
BGP is not used for VPC-to-VPC routing in Transit Gateway.
- ✗
ECMP routing is enabled, causing traffic to be load-balanced across multiple paths.
Why it's wrong here
ECMP distributes traffic across equal-cost paths, not suboptimal routing.
- ✓
Incorrect route table associations and propagations in the Transit Gateway.
Why this is correct
Route tables determine which attachments can reach each other.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services 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 ANS-C01 exam.