A security engineer has designed a VPC to segment private traffic from public traffic.

In a properly segmented VPC architecture, public subnets route internet-bound traffic to an internet gateway, while private subnets route outbound internet traffic through a NAT gateway that resides in a public subnet. According to the AWS Certified Security – Specialty Official Study Guide and Amazon VPC documentation, private subnets must never have a direct route to an internet gateway.

The issue described indicates that private subnets are incorrectly routing traffic directly to the internet gateway. To remediate this, a NAT gateway must be provisioned in each public subnet to ensure high availability across Availability Zones. This satisfies the requirement that private resources can initiate outbound connections without being directly reachable from the internet.

Next, the route tables associated with the private subnets must be updated so that the default route (0.0.0.0/0) points to the NAT gateway in the same Availability Zone. This ensures proper traffic flow and prevents cross-AZ dependencies.

Option B is incorrect because NAT gateways must reside in public subnets. Option C is unnecessary because local routes to the VPC CIDR range are automatically created. Option E is explicitly insecure, as it would reintroduce direct internet gateway access from private subnets.

AWS documentation consistently identifies NAT gateways plus correct private subnet routing as the standard design for secure VPC segmentation.

AWS Certified Security – Specialty Official Study Guide

Amazon VPC Route Table Documentation

AWS Well-Architected Framework – Security Pillar