ANS-C01 Network Security, Compliance and Governance Practice Question
A company has a VPC with public and private subnets. The private subnets need to access the internet through a NAT gateway. The security team wants to ensure that traffic from the private subnets cannot bypass the NAT gateway. Which configuration should be used?
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 route in the private subnet route table with destination 0.0.0.0/0 pointing to the NAT gateway
A route table with a default route (0.0.0.0/0) pointing to the NAT gateway ensures all outbound traffic from private subnets goes through the NAT gateway, preventing bypass. Option A is wrong because a forward proxy in a public subnet would still require routing and does not enforce the NAT gateway path. Option B is wrong because an egress-only internet gateway is for IPv6 only. Option D is wrong because a security group on the NAT gateway controls allowed traffic but does not enforce routing.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Deploy a forward proxy in a public subnet and configure the private subnets to use it
Why it's wrong here
This still requires routing to the proxy, and the proxy itself must have a route to the internet.
- ✗
Use an egress-only internet gateway for the private subnets
Why it's wrong here
Egress-only internet gateways are for IPv6 traffic only.
- ✓
Add a route in the private subnet route table with destination 0.0.0.0/0 pointing to the NAT gateway
Why this is correct
This forces all outbound traffic to go through the NAT gateway.
- ✗
Attach a security group to the NAT gateway that only allows outbound traffic
Why it's wrong here
Security groups do not enforce routing; they only filter traffic.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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