For the strongest protection of infrastructure devices, where should access lists be deployed?

Deploying access lists in the ingress direction on all IP-configured interfaces provides the strongest protection for infrastructure devices because it allows for the filtering of incoming traffic before it reaches the device's core operating processes. This proactive approach enables network administrators to define and enforce security policies that can block potentially harmful traffic right at the entry point.

By applying access lists to control what ingress traffic is permitted, administrators can effectively mitigate risks from untrusted sources, limit exposure to vulnerabilities, and reduce the likelihood of unauthorized access attempts. Filtering in the ingress direction ensures that only legitimate and explicitly allowed traffic is allowed into the device, providing an essential layer of security that is critical in protecting network infrastructure from various threats.

Using access lists exclusively on egress interfaces, on the other hand, would permit unwanted traffic to reach the device before it is filtered out, which does not provide the same level of security. Moreover, restricting access lists to only specific interface types, such as loopback or VLAN interfaces, limits their protective benefit to only part of the network path, thereby increasing vulnerability in other areas. The greatest overall defense mechanism involves deploying access lists at the ingress of all IP-configured interfaces to create a comprehensive security posture.