ACP-Cloud1 Exam Dumps : ACP Cloud Computing Certification

RDS provides whitelist access policies. You can set permitted IP addresses and IP network segments to effectively prevent hackers from attacking the server by port scanning1. A whitelist is a list of IP addresses or CIDR blocks that are allowed to access an RDS instance. By default, the whitelist is empty, which means that no IP address can access the RDS instance. You can add IP addresses or CIDR blocks to the whitelist to allow access from specific sources. You can also modify or delete the whitelist as needed2. Whitelist access policies help improve the security of your RDS instance and protect your data from unauthorized access3. 

In Alibaba Cloud RDS, multiple databases can be created within a single instance, allowing users to manage different databases under one RDS instance efficiently. However, databases within the same instance must have unique names, and resources such as CPU and memory are shared across databases within the same instance, contrary to the options provided in answers B and C.

According to the Alibaba Cloud Academy, a VPC is an isolated network environment that is completely isolated from each other. Each VPC has an independent tunnel ID, and a tunnel ID corresponds to a virtualized network. This means that different VPCs cannot communicate with each other through the tunnel ID. Subnets are not divided like the traditional network environment, but rather are logical divisions of the VPC. Different cloud servers within each subnet are connected by the same router, but different subnets are interconnected by route tables, not switches. ECS instances in a VPC use security group firewalls for Layer 4 network access control, not Layer 2. The internal networks of different VPCs are completely isolated and can be interconnected through IP addresses mapped to the outside, such as NAT Gateway or EIP. References: ACP Cloud Computing Certification Preparation Course - Internetworking with VPC, Alibaba Cloud VPC User Guide