The basic configuration files, the kernel configuration file, the startup files, and the /etc/inetd.conf or /etc/xinetd.conf file are necessary for installing the TCP/IP software on a Unix system. The kernel comes configured to run TCP/IP on most systems. Some systems, such as Solaris, are designed to eliminate kernel configuration. Others, such as Linux, encourage it as a way to produce a more efficient kernel. In either case, a network administrator needs to be aware of the kernel configuration commands required for TCP/IP so that they are not accidentally removed from the kernel when it is rebuilt.
Network services are either started at boot time from a startup
script or are started on demand using xinetd or inetd. BSD systems have a few startup scripts
that are run in sequence for every boot. System V Unix runs a different
set of startup scripts for each runlevel. Runlevels are used to start
the system in different modes, e.g., single user mode or multi-user
mode. Both Solaris and Linux use the System V startup scheme.
inetd and xinetd start essential network services. Most
Unix systems use inetd, although
some, such as Red Hat Linux, use xinetd. Reconfigure inetd or xinetd to add new services and to improve
security. Security can be improved by removing unneeded services or by
adding access control. Chapter 12
provides additional information on how inetd and xinetd are used to improve system
security.
The kernel configuration defines the network interface. In the next chapter we configure it, calling upon the planning we did in Chapter 4.