5.9 Violation is defined in this context to refer to the act of someone gaining access to a system or data that they are not authorized to access. 5.10 Screening is defined as determining if communications traffic may pass through a network device based solely on destination and source information of the network packet containing the data. Screening in this context implies their is no authentication of the actual originator of the data. 5.11 Authentication is defined as the act of requiring the 'person' requesting access to a network, LAN, or system to identify themselves through one or more identification schemes. Screening only makes decisions based on source and destination addresses.
Authentication makes decisions based on 'who' was at the source.
The firewall shields a system from potential attacks by unauthorized individuals. That is, the network responsibility ends at the router port to which the agency LAN is connected. It is important to remember, any network or system can be violated given enough time. Therefore, any security strategy must take into account how to detect the fact that a violation is in process or has occurred, hence the need for auditing and proper backups. An agency must always assume the network is unsafe when preparing their security policies.