Network Functions - Red Hat LINUX 7.2 Reference Manual

Section 12.3:Network Functions 189
In order to bring a particular interface up or down properly, these scripts may call one another to provide
a certain type of functionality. In addition, other scripts will find their way into the /etc/syscon-
fig/network-scripts directory as software is installed that requires a new type of interface. Be
aware that removing or modifying these scripts can cause various interface connections to act strangely
or fail, as these scripts tend to rely on each other. However, advanced users can modify scripts linked
with a specific interface to make additional steps occur when that interface is brought up or down.
You can also use the init script /etc/rc.d/init.d/network to activate and deactive all network
interfaces configured to start at boot time with the command:
/sbin/service network action
where action is either start to start the network interfaces, stop to stop the network interfaces, or
restart to restart the network interfaces. You can also use the command /sbin/service/net-
work status to view a list of configured devices and currently active devices.
Instructions for making interfaces active and inactive, through the use of the command line or GUI-
based administration tools, can be found in the Official Red Hat Linux Customization Guide.

12.3 Network Functions

Red Hat Linux makes use of several files that contain important functions that are used in various
ways to bring interfaces up and down. Rather than forcing each interface control file to contain the
same functions as another, these functions are conveniently grouped together in a few files that can be
sourced when needed. If you are altering your interface control files for particular reasons, it may be
well worth it to also group common functions in these files.
The most common network functions file is network-functions, located in the
/etc/sysconfig/network-scripts directory. This file contains a variety of com-
mon IPv4 functions useful to many interface control scripts, such as contacting running programs
that have requested information about changes in an interface's status, setting host names, finding a
gateway device, seeing if a particular device is down or not, and adding a default route.
As the functions required for IPv6 interfaces are different than IPv4 interfaces, a network-func-
tions-ipv6 file exists specifically to hold this information. IPv6 support must be enabled in the
kernel in order to communicate via that protocol. A function is present in this file that checks for the
presence of IPv6 support. Additionally, functions that configure and delete static IPv6 routes, create
and remove tunnels, add and remove IPv6 addresses to an interface, and test for the existence of an
IPv6 address on an interface can also be found in this file.