If the packet has not already been dropped, JUNOS software with enhanced services performs session lookup to determine whether the packet belongs to an existing session. The system uses six match criteria to perform the session lookup:
If the packet does not match an existing session, the system creates a new session for it. This process is called the first-packet path. (See First-Packet Path Processing.)
If the packet matches a session, fast-path processing is performed. (See Fast-Path Processing.)