Why is the order of rules important in a packet filter firewall?

The order of rules in a packet filter firewall is crucial primarily to prevent rule conflicts. Firewalls process rules in a sequential manner, meaning that the first rule that matches a packet will dictate the action taken (either to allow or block the packet). If overlapping or conflicting rules are not carefully ordered, it can lead to unexpected behavior, where certain packets might be allowed or denied inappropriately, resulting in security holes or access issues.

For example, if a more permissive rule comes before a stricter one, packets that should be blocked may instead be allowed. Therefore, properly structuring the order of rules helps ensure that the intended policies are enforced correctly, maintaining a clear and functional security posture.

While other factors like security, processing speed, and user-defined policies are relevant considerations, they do not directly relate to the immediate necessity of avoiding conflicts among rules in a packet filter firewall's operational logic.