TCP Wrappers is enabled on SIMP systems. TCP Wrappers is a host-based networking ACL system, used to filter access to IP addresses. It allows host or subnetwork IP addresses, names and/or ident query replies, to be used as tokens on which to filter for access control purposes.
TCP Wrappers uses the /etc/hosts.allow and the /etc/hosts.deny files to configure the access control.
References: AC-4