What it covers. NIST guidance on firewall technologies and how to select, configure and manage them. It explains types of firewalls, their placement in network architectures and the development and maintenance of firewall policy.
In practice. Applying it well means a documented firewall policy based on deny by default, rules that are justified and owned, and regular reviews to remove unused or overly broad rules. Changes go through change management and firewall logs are retained and monitored. Evidence includes rule sets with justifications, review records and change history.
Common gaps. Common gaps are years of accumulated rules with no owner, broad any-to-any rules and no review after projects end. The publication dates from 2009, so it does not cover cloud-native controls in depth.