Palo Alto Session Logging

The terms “Log at Session Start” and “Log at Session End” are used to describe the practice of creating logs or records at the beginning and end of a session, respectively. Sessions here can refer to any process or activity that has a defined start and end, such as user sessions in web applications, network sessions, or any computing or processing sessions. Here’s the importance of both and when they might be used:

1. Log at Session Start:

  • Tracking Resources: Logging at the start of a session helps track which resources are being used. This information can be critical in resource allocation and management. 
  • Debugging: If a session fails to start correctly or experiences issues early on, having logs from the start helps diagnose what might have gone wrong. 
  • User Activity: In web applications, logging at the start of a user session can help in user analytics and behavior tracking, which can help improve the user experience or security monitoring.
  • Audit Trail: Creating a log at the start of a session helps create an audit trail which can be important for compliance with various regulations and standards.

2. Log at Session End:

  • Performance Monitoring: Logging at the end of a session can help monitor the performance of an application or system by recording how much time was taken and which resources were used.   
  • Error Tracking: If any errors or exceptions occur during a session, logging at the end can help record such events for future analysis.   
  • User Behavior Analysis: For web applications, logging at the end of a session can provide insights into user behavior, such as which features were used, and how the user interacted with the application.   
  • Cleaning Up: Sometimes, it’s necessary to perform specific clean-up actions at the end of a session, such as releasing resources. Logging at this stage ensures there’s a record that these actions were performed.

It is important to note that logging at both session start and session end is generally not recommended by Palo Alto Networks due to the potential impact on the management plane’s CPU.

Best Practices from Palo Alto Networks

Palo Alto Networks, a global leader in cybersecurity solutions, recommends logging at session end for regular logging purposes. By capturing logs at the end of a session, organizations can obtain a comprehensive record of the session, including any application changes that occurred. Palo Alto Networks emphasizes recognizing and adapting to dynamic application behavior to ensure accurate security policies and analysis.

Palo Alto Networks also highlights that firewalls analyze sessions for vulnerabilities or malicious files in a typical configuration. When identified, the firewall generates logs for the identification and may close the session accordingly, depending on the configuration. If the goal is to monitor long-running sessions, logging at session start may not provide additional information through traffic logs. Monitoring the current session’s traffic using techniques like NetFlow monitoring or SNMP/API monitoring of the session table is recommended for actionable information.

Beware of Logs Filling Up Too Quickly

While comprehensive logging is essential, organizations should be cautious about logs filling up rapidly. Consider the following implications:

  • Performance Impact: Excessive storage consumption by logs can degrade system performance, leading to delays or service interruptions.
  • Data Loss: Overwriting older logs with new ones can result in losing important data, hindering investigations and compliance efforts.
  • Increased Storage Costs: Managing large log volumes requires additional storage resources, leading to higher infrastructure costs.

To mitigate these challenges, implement the following practices:

  • Selective Logging: Log only necessary information and avoid excessive detail irrelevant to security analysis or compliance requirements.
  • Log Size Monitoring: Regularly monitor log sizes to address potential storage issues proactively. Archive or delete old logs based on retention policies and regulatory requirements.
  • Log Rotation: Employ log rotation mechanisms to ensure continuous logging without overwhelming storage capacity. This involves archiving older logs and starting new log files as needed.


Effective session logging, particularly at session end as recommended by Palo Alto Networks, provides valuable insights into application changes and ensures proper security policy enforcement. Striking a balance between comprehensive logging and potential performance and storage implications is crucial. Organizations can derive maximum value from session logging by following best practices and employing prudent log management strategies while mitigating potential challenges.