Controlling Access to Services

As a security measure, most network services are managed by a protective program called a TCP wrapper. The protected services are those listed in /etc/inetd.conf that specify /usr/sbin/tcpd. tcpd can allow or deny access to a service based on the origin of the request, and the configuration in /etc/hosts.allow and /etc/hosts.deny.

By default Red Hat Linux allows all service requests. To disable or limit services you can edit /etc/hosts.allow. Here is an example /etc/hosts.allow file:

in.talkd: ALL
in.ntalkd: ALL
in.fingerd: ALL
in.ftpd: ALL

This configuration allows all connections from and * machines. It also allows talk, finger, and FTP requests from all machines.

tcpd allows much more sophisticated access control, using a combination of /etc/hosts.allow and /etc/hosts.deny. Read the tcpd(8) and hosts_access(5) man pages for complete details.