Implementation of a firewall can be a complex process, with multiple factors affecting the overall security effectiveness of the solution. These should be considered over the course of the useful life of the solution, including:

Deployment use cases—Will the firewall be deployed to protect servers or desktop clients, or both?; Defensive capabilities in the deployment use cases; Relevant evasions (i.e., IP Address spoof and TCP split handshake); Device stability and reliability; and overall manageability.