21.2. TCP Wrappers

Many UNIX system administrators are accustomed to using TCP wrappers to manage access to certain network services. Any network services managed by xinetd (as well as any program with built-in support for libwrap) can use TCP wrappers to manage access. xinetd can use the /etc/hosts.allow and /etc/hosts.deny files to configure access to system services. As the names imply, hosts.allow contains a list of rules that allow clients to access the network services controlled by xinetd, and hosts.deny contains rules to deny access. The hosts.allow file takes precedence over the hosts.deny file. Permissions to grant or deny access can be based on individual IP address (or hostnames) or on a pattern of clients. Refer to the Red Hat Enterprise Linux Reference Guide and hosts_access in section 5 of the man pages (man 5 hosts_access) for details.

21.2.1. xinetd

To control access to Internet services, use xinetd, which is a secure replacement for inetd. The xinetd daemon conserves system resources, provides access control and logging, and can be used to start special-purpose servers. xinetd can be used to provide access only to particular hosts, to deny access to particular hosts, to provide access to a service at certain times, to limit the rate of incoming connections and/or the load created by connections, and more

xinetd runs constantly and listens on all ports for the services it manages. When a connection request arrives for one of its managed services, xinetd starts up the appropriate server for that service.

The configuration file for xinetd is /etc/xinetd.conf, but the file only contains a few defaults and an instruction to include the /etc/xinetd.d directory. To enable or disable an xinetd service, edit its configuration file in the /etc/xinetd.d directory. If the disable attribute is set to yes, the service is disabled. If the disable attribute is set to no, the service is enabled. You can edit any of the xinetd configuration files or change its enabled status using the Services Configuration Tool, ntsysv, or chkconfig. For a list of network services controlled by xinetd, review the contents of the /etc/xinetd.d directory with the command ls /etc/xinetd.d.