1. At least one computer-readable storage medium having encoded thereon computer-executable instructions which, when executed, perform a method, wherein the at least one computer-readable storage medium is not a signal, the method comprising: retrieving a plurality of firewall policies that are enforced by respective different firewalls of respective different devices on the network, each firewall policy comprising one or more firewall rules, the firewall policies including a target firewall policy of a target firewall of a target device, the target firewall policy having higher or lower precedence relative to another of the firewall policies; merging the retrieved firewall policies into a merged firewall policy that includes firewall rules corresponding to each of the retrieved firewall policies; and receiving a new firewall rule, the new firewall rule specifying a communication allowance or disallowance, and automatically determining, according to the merged security policy, whether the communication allowance or disallowance will be effected for the target device if the new firewall rule is applied to the target firewall policy and implemented by the target firewall.