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.