When configuring ACLs, which method is considered a good practice?

When configuring Access Control Lists (ACLs), using a whitelist approach where only the required traffic is permitted is considered a good practice. This method enhances security by minimizing the attack surface. By explicitly allowing only the necessary services and protocols, you ensure that any potentially harmful or unwanted traffic is denied by default.

The whitelist approach operates on the principle of least privilege, which is a key security guideline. When network devices are configured to accept only specific traffic, it reduces the risk of unauthorized access and helps protect sensitive data. This practice is particularly effective in environments where compliance with security standards is critical, as it promotes a proactive stance on security rather than a reactive one.

In contrast, while the blacklist method allows for broader access and only restricts specific ports, it may inadvertently leave other vulnerabilities open. Not needing ACLs at all undermines network security by allowing unrestricted access, which is typically not advisable in most network environments. Furthermore, limiting ACL usage strictly to the perimeter of the network can create blind spots and doesn't provide comprehensive security throughout the network architecture. Overall, whitelisting provides a more structured and secure approach to network traffic management.