ANS-C01 Network Design Practice Question
A company is planning to connect multiple VPCs in different AWS accounts using AWS Transit Gateway. The VPCs must be able to communicate with each other, but the company wants to centralize egress traffic to the internet through a single VPC that has a NAT gateway. Which configuration meets these requirements?
⚠ Common exam trap
It's easy for candidates to confuse VPC peering with Transit Gateway, assuming VPC peering supports transitive routing (which it does not), or they think placing a NAT gateway in each VPC is acceptable, missing the explicit requirement for centralized egress.
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
✓
Attach all VPCs to a Transit Gateway, create a central egress VPC with a NAT gateway, and configure Transit Gateway route tables to send default traffic to the central VPC.
AWS Transit Gateway allows you to attach multiple VPCs from different accounts and centrally manage routing. By configuring the Transit Gateway route tables to send default traffic (0.0.0.0/0) to a central egress VPC that contains a NAT gateway, all other VPCs can route internet-bound traffic through that single NAT gateway, centralizing egress while maintaining inter-VPC communication.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Attach all VPCs to a Transit Gateway, create a central egress VPC with a NAT gateway, and configure Transit Gateway route tables to send default traffic to the central VPC.
Why this is correct
Centralizes internet egress while allowing VPC-to-VPC communication.
- ✗
Use AWS Site-to-Site VPN to connect the VPCs and route traffic through a central VPN endpoint.
Why it's wrong here
Unnecessary complexity and not designed for VPC-to-VPC connectivity.
- ✗
Use VPC peering to connect all VPCs and configure a NAT gateway in one VPC.
Why it's wrong here
VPC peering is not transitive; each pair needs a peering connection.
- ✗
Attach each VPC to a Transit Gateway and configure a NAT gateway in each VPC.
Why it's wrong here
This is not centralized egress.
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