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.