Installation guide

Chapter 12. Network Scripts 163
Warning
Never edit the loopback interface script, /etc/sysconfig/network-scripts/ifcfg-lo, by hand.
Doing so can prevent the system from operating correctly.
An infrared interface allows information between devices, such as a laptop and a printer, to flow over
an infrared link which works in a similar way to an Ethernet device except that it commonly occurs
over a peer-to-peer connection.
A Parallel Line Interface Protocol (PLIP) connection works much the same way, except that it utilizes
a parallel port.
Token Ring topologies are not as common on Local Area Networks as they once were, having been
eclipsed by Ethernet.
12.2.4. Alias and Clone Files
Two lesser-used types of interface configuration files found in the /etc/sysconfig/network-
scripts/ directory are alias and clone files.
Alias interface configuration files take names in the format of ifcfg-
if-name : alias-
value
, and they allow an alias to point to an interface. For example, a ifcfg-eth0:0 file could
be configured to specify DEVICE=eth0:0 and a static IP address of 10.0.0.2, serving as an alias of
an Ethernet interface already configured to receive its IP information via DHCP in ifcfg-eth0. At
that point, the eth0 device is bound to a dynamic IP address, but it can always be referred to on that
system via the fixed 10.0.0.2 IP address.
A clone interface configuration file should follow this naming convention, ifcfg- if-name -
clone-name . While an alias file is another way to refer to an existing interface configuration file,
a clone file is used to specify additional options when specifying an interface. For example, if you
have a standard DHCP Ethernet interface called eth0, it may look similar to this:
DEVICE=eth0
ONBOOT=yes
BOOTPROTO=dhcp
Since USERCTL is set to no if it is not specified, users cannot bring this interface up and down. To
give users this ability, create a clone by copying ifcfg-eth0 to ifcfg-eth0-user and add the
following line:
USERCTL=yes
When a user brings up the eth0 interface with the ifup eth0-user command, the configuration op-
tions from ifcfg-eth0 and ifcfg-eth0-user are conmbined. While this is a very basic example,
this method can be used with a variety of options and interfaces.
The easiest way to create alias and clone interface configuration files is to use the graphical network
configuration tool, Network Administration Tool. For more on using this tool, see the chapter called
Network Configuration in the Official Red Hat Linux Customization Guide.
12.3. Interface Control Scripts
The interface control scripts activate and deactivated system interfaces. There are two primary in-
terface control scripts, /sbin/ifdown and /sbin/ifup, that call on control scripts located in the
/etc/sysconfig/network-scripts/ directory.