AWS Certified Advanced Networking Specialty Practice Exam

If you can't add a Classless Inter-Domain Routing (CIDR) range to an existing VPC, what could resolve the issue?

1. Upgrading your AWS account

2. Deleting unused routes if at maximum allowed

3. Recreating the VPC

4. Changing your network access control list

The correct answer is: Deleting unused routes if at maximum allowed

To understand why deleting unused routes is a viable solution for the issue of not being able to add a CIDR range to an existing VPC, it's essential to consider the limitations in AWS regarding the management of VPCs. When a VPC reaches its limit for routes or has unused routes that clutter the route table, it may lead to complications when trying to add additional CIDR blocks. Each VPC has limits on the number of route table entries. If this limit has been reached, further additions—including CIDR ranges—would not be permissible until some of the existing routes are removed. By deleting unused routes, you free up space within the route table, thereby creating the opportunity to successfully add new CIDR ranges. This management of resources is crucial for optimal networking within AWS. In contrast, other options typically won't resolve the issue directly. Upgrading your AWS account may expand certain limits for resources but doesn't specifically address route table limitations. Recreating the VPC would involve significant overhead, as it erases existing configurations, and changing the network access control list doesn't directly relate to the CIDR addition process. Hence, refining the route table by removing unnecessary routes is the most effective solution in this scenario.