Security Policy

Security policy protects network assets from threats and disruptions and aids in optimally allocating network resources for enhancing productivity and efficiency in business processes. On a Palo Alto Networks firewall, individual Security policy rules determine whether to block or allow a session based on traffic attributes, such as the source and destination security zone, the source and destination IP address, the application, the user, and the service.
To ensure that end users authenticate when they try to access your network resources, the firewall evaluates Authentication Policy before Security policy.
All traffic passing through the firewall is matched against a session and each session is matched against a Security policy rule. When a session match occurs, the firewall applies the matching Security policy rule to bidirectional traffic in that session (client to server and server to client). For traffic that doesn’t match any defined rules, the default rules apply. The default rules—displayed at the bottom of the security rulebase—are predefined to allow all intrazone (within the zone) traffic and deny all interzone (between zones) traffic. Although these rules are part of the pre-defined configuration and are read-only by default, you can override them and change a limited number of settings, including the tags, action (allow or block), log settings, and security profiles. You can View Policy Rule Usage to determine when and how many times traffic matches the security policy rule to determine the effectiveness of the rule.
Security policy rules are evaluated left to right and from top to bottom. A packet is matched against the first rule that meets the defined criteria and, after a match is triggered, subsequent rules are not evaluated. Therefore, the more specific rules must precede more generic ones in order to enforce the best match criteria. Traffic that matches a rule generates a log entry at the end of the session in the traffic log if you enable logging for that rule. The logging options are configurable for each rule and can, for example, be configured to log at the start of a session instead of, or in addition to, logging at the end of a session.

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