ANS-C01 Network Implementation Practice Question
A company is using AWS Transit Gateway to interconnect multiple VPCs and on-premises networks. The network engineer needs to ensure that traffic between VPC A and VPC B follows a specific path through a Network Virtual Appliance (NVA) in VPC C. Which TWO actions should the engineer take?
⚠ Common exam trap
A common mix-up: candidates think enabling route propagation (Option C) is sufficient for traffic inspection, but it actually allows direct routing between VPCs, bypassing the NVA, unless specific static routes are added to override the propagated routes.
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
✓
Add a static route in the Transit Gateway route table for VPC A's CIDR pointing to the VPC B attachment with a blackhole.
Adding a static route in the Transit Gateway route table for VPC A's CIDR pointing to the VPC B attachment with a blackhole forces traffic destined to VPC B to be dropped at the Transit Gateway, preventing direct routing. Option D is correct because adding a specific route for VPC B's CIDR in the Transit Gateway route table used by VPC A, pointing to the VPC C attachment, ensures traffic from VPC A to VPC B is forwarded through the NVA in VPC C, enforcing the desired inspection path.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Associate VPC A's and VPC B's route tables with a different Transit Gateway route table that has a default route pointing to the VPC C attachment.
Why it's wrong here
This would affect all traffic, not just between A and B.
- ✓
Add a static route in the Transit Gateway route table for VPC A's CIDR pointing to the VPC B attachment with a blackhole.
Why this is correct
This prevents VPC A from directly reaching VPC B via the Transit Gateway.
- ✗
Enable route propagation for VPC A and VPC B attachments in the same Transit Gateway route table.
Why it's wrong here
Propagation would automatically add routes, potentially allowing direct communication.
- ✓
Add a specific route for VPC B's CIDR in the Transit Gateway route table used by VPC A, pointing to the VPC C attachment.
Why this is correct
This sends traffic destined to VPC B through VPC C.
- ✗
Create a VPC peering connection between VPC A and VPC B.
Why it's wrong here
VPC peering would allow direct connectivity, bypassing the NVA.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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