You can view logs of the traffic passing through the BIG-IP system using the reporting feature in Policy Enforcement Manager (PEM).
The logs can be either session-based or flow-based. Session-based logs provide information about the session, while flow-based logs contain information about the traffic flow.
In Policy Enforcement Manager, reporting provides a default format. The default format can be changed by defining a format script, which enables you to add your own text and fields, and customize the log messages you would like to see in the logging server.
For example, you can create a format script for session reporting by typing: return "(session bytes-in:[PEM::session stats reported bytes-in]). The iRules command retrieves the value of the attribute, bytes-in, in session record.
Similarly, you can create a format script for flow reporting by typing: return "(flow bytes-in:[PEM::flow stats reported bytes-in]). The iRules command retrieves the value of the attribute, bytes-in, in flow record.