Manage Custom or Unknown Applications
Palo Alto Networks provides weekly application updates to identify new App-ID signatures. By default, App-ID is always enabled on the firewall, and you don't need to enable a series of signatures to identify well-known applications. Typically, the only applications that are classified as unknown traffic—tcp, udp or non-syn-tcp—in the ACC and the traffic logs are commercially available applications that have not yet been added to App-ID, internal or custom applications on your network, or potential threats.
On occasion, the firewall may report an application as unknown for the following reasons:
Incomplete data—A handshake took place, but no data packets were sent prior to the timeout. Insufficient data—A handshake took place followed by one or more data packets; however, not enough data packets were exchanged to identify the application.
The following choices are available to handle unknown applications:
Create security policies to control unknown applications by unknown TCP, unknown UDP or by a combination of source zone, destination zone, and IP addresses. Request an App-ID from Palo Alto Networks—If you would like to inspect and control the applications that traverse your network, for any unknown traffic, you can record a packet capture. If the packet capture reveals that the application is a commercial application, you can submit this packet capture to Palo Alto Networks for App-ID development. If it is an internal application, you can create a custom App-ID and/or define an application override policy. Create a Custom Application with a signature and attach it to a security policy, or create a custom application and define an application override policy—A custom application allows you to customize the definition of the internal application—its characteristics, category and sub-category, risk, port, timeout—and exercise granular policy control in order to minimize the range of unidentified traffic on your network. Creating a custom application also allows you to correctly identify the application in the ACC and traffic logs and is useful in auditing/reporting on the applications on your network. For a custom application you can specify a signature and a pattern that uniquely identifies the application and attach it to a security policy that allows or denies the application.
Alternatively, if you would like the firewall to process the custom application using fast path (Layer-4 inspection instead of using App-ID for Layer-7 inspection), you can reference the custom application in an application override policy rule. An application override with a custom application will prevent the session from being processed by the App-ID engine, which is a Layer-7 inspection. Instead it forces the firewall to handle the session as a regular stateful inspection firewall at Layer-4, and thereby saves application processing time.
For example, if you build a custom application that triggers on a host header www.mywebsite.com, the packets are first identified as web-browsing and then are matched as your custom application (whose parent application is web-browsing). Because the parent application is web-browsing, the custom application is inspected at Layer-7 and scanned for content and vulnerabilities.
If you define an application override, the firewall stops processing at Layer-4. The custom application name is assigned to the session to help identify it in the logs, and the traffic is not scanned for threats.

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