Explanation
Logging for a security policy can be configured to generate log entries at session initialization, at session close, or both. Logging at session initialization records the initial packet that matches the policy and triggers the session creation. Logging at session close records the summary statistics of the session, such as bytes and packets transmitted and received, and the reason for session termination. Logging at session initialization and close provides the most complete information about the traffic that matches the policy. Logging at fixed intervals, such as every 10 minutes or every 60 seconds, is not supported by Junos OS security policies. References:
Security, Professional (JNCIP-SEC) Exam Objectives, Firewall Filters section Junos OS Security Configuration Guide, Understanding Security Policy Logging section Advanced Juniper Security (AJSEC) Course, Chapter 4: Advanced Logging and Reporting