The basic building block of a sound security plan is a firewall. The firewall monitors and controls traffic between two separate networks; it acts as a barrier while utilizing specific rules to assure that only the network traffic you want reaches your systems. Rules can be used to restrict access by IP, port, protocol, or the like. A firewall is a static, basic level of security, but is a simple way to manage a large number of potential security threats by substantially reducing public access to certain systems or applications. It is a required component of most compliance standards.