When you create a policy, you must specify an application, or service, for it to indicate that the policy applies to traffic of that type. Sometimes the same applications or a subset of them can be present in multiple policies, making it difficult to manage. JUNOS Software allows you to create groups of applications called application sets. Application sets simplify the process by allowing you to manage a small number of application sets, rather than a large number of individual application entries.
The application (or application set) is referred to by security policies as match criteria for packets initiating sessions. If the packet matches the application type specified by the policy and all other criteria match, then the policy action is applied to the packet.
Before You Begin
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You can specify the name of an application set in a policy. In this case, if all of the other criteria match, any one of the applications in the application set serves as valid matching criteria; any is the default application name that indicates all possible applications.
Applications are created in the .../applications/application/<application-name> directory. You do not need to configure an application for any of the services that are predefined by the system.
In addition to predefined services, you can configure a custom service. After you create a custom service, you can refer to it in a policy.