When should a security appliance be implemented in a network?

A security appliance should be implemented in a network specifically when there is a change in the trust level in the network. This is because changes in trust levels, such as introducing new devices, users, or network zones, can create vulnerabilities that need to be addressed to maintain the integrity, confidentiality, and availability of network resources. A security appliance, such as a firewall or intrusion detection system, is crucial to enforce security policies and monitor traffic in these scenarios.

When trust levels change, it often indicates that additional security measures are necessary to protect against potential threats that could arise from less trusted areas of the network, or from an external environment.

Deploying a security appliance at this stage helps ensure that appropriate security controls are in place before any sensitive data flows across the network or new communications occur, making it a proactive measure rather than a reactive one.