ANS-C01 Network Implementation Practice Question
A company is building a hybrid network with an AWS Transit Gateway connecting multiple VPCs and an on-premises network via Direct Connect. The on-premises network uses BGP to advertise routes to the Transit Gateway. One of the VPCs has an overlapping CIDR (10.0.0.0/16) with the on-premises network (10.0.0.0/8). The company wants to ensure that traffic from other VPCs to 10.0.0.0/16 goes to the VPC, not on-premises. What configuration is required?
⚠ Common exam trap
Many candidates think BGP attributes like AS_PATH prepending are needed to influence route preference, forgetting that the longest prefix match rule takes precedence over any BGP path selection attribute.
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
✓
No additional configuration is needed; the more specific route will be preferred automatically
AWS Transit Gateway route tables follow the longest prefix match rule. The VPC advertises 10.0.0.0/16, which is a more specific route than the on-premises 10.0.0.0/8. Therefore, traffic destined for 10.0.0.0/16 will automatically be forwarded to the VPC attachment without any additional configuration.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use AS_PATH prepending on the on-premises BGP advertisements to make them less preferred
Why it's wrong here
Incorrect; AS_PATH prepending affects BGP path selection but longest prefix match overrides it.
- ✓
No additional configuration is needed; the more specific route will be preferred automatically
Why this is correct
Correct; Transit Gateway uses longest prefix match, so the /16 from VPC is preferred over /8 from on-premises.
- ✗
Add a static route in the Transit Gateway route table for 10.0.0.0/16 pointing to the VPC attachment
Why it's wrong here
Incorrect; the more specific route from the VPC attachment is already preferred.
- ✗
Disable route propagation from the Direct Connect virtual interface to the Transit Gateway
Why it's wrong here
Incorrect; disabling propagation would remove the on-premises routes completely, which may not be desired.
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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.