1. A method comprising: providing, by a network security appliance, a security rule configuration interface through which a network administrator can specify parameters of security rules to be applied to network traffic attempting to traverse the network security appliance through one or more of a plurality of interfaces of the network security appliance; receiving, by the network security appliance via the security rule configuration interface, interface information defining a traffic flow to be controlled by a security rule of the security rules, wherein the interface information specifies (i) a first set of multiple interfaces, representing a proper subset of the plurality of interfaces, as a source interface of the traffic flow; and (ii) a second set of multiple interfaces, representing a proper subset of the plurality of interfaces, as a destination interface of the traffic flow such that the security rule allows multiple selections for the source interface and multiple selections for the destination interface; receiving, by the network security appliance via the security rule configuration interface, information regarding an action to be performed on the network traffic when the network traffic matches the security rule; storing, by the network security appliance, the security rule as part of a rule set to be applied to the network traffic.