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8.2. Interface Configuration Files
Interface configuration files control the software interfaces for individual network devices. As the system boots, it uses these files to determine what interfaces to bring up and how to configure them. These files are usually named
ifcfg-<name>, where <name> refers to the name of the device that the configuration file controls.
8.2.1. Ethernet Interfaces
One of the most common interface files is
ifcfg-eth0, which controls the first Ethernet network interface card or NIC in the system. In a system with multiple NICs, there are multiple ifcfg-eth<X> files (where <X> is a unique number corresponding to a specific interface). Because each device has its own configuration file, an administrator can control how each interface functions individually.
The following is a sample
ifcfg-eth0 file for a system using a fixed IP address:
DEVICE=eth0 BOOTPROTO=none ONBOOT=yes NETWORK=10.0.1.0 NETMASK=255.255.255.0 IPADDR=10.0.1.27 USERCTL=no
The values required in an interface configuration file can change based on other values. For example, the
ifcfg-eth0 file for an interface using DHCP looks quite a bit different because IP information is provided by the DHCP server:
DEVICE=eth0 BOOTPROTO=dhcp ONBOOT=yes
The Network Administration Tool (
system-config-network) is an easy way to make changes to the various network interface configuration files (refer to the chapter titled Network Configuration in the System Administrators Guide for detailed instructions on using this tool).
However, it is also possible to edit the configuration files for a given network interface manually.
Below is a listing of the configurable parameters in an Ethernet interface configuration file:
BOOTPROTO=<protocol>, where<protocol>is one of the following:none— No boot-time protocol should be used.bootp— The BOOTP protocol should be used.dhcp— The DHCP protocol should be used.
BROADCAST=<address>, where<address>is the broadcast address. This directive is deprecated, as the value is calculated automatically withipcalc.DEVICE=<name>, where<name>is the name of the physical device (except for dynamically-allocated PPP devices where it is the logical name).DHCP_HOSTNAME— Only use this option if the DHCP server requires the client to specify a hostname before receiving an IP address. (The DHCP server daemon in Red Hat Enterprise Linux does not support this feature.)DNS{1,2}=<address>, where<address>is a name server address to be placed in/etc/resolv.confif thePEERDNSdirective is set toyes.ETHTOOL_OPTS=<options>, where<options>are any device-specific options supported byethtool. For example, if you wanted to force 100Mb, full duplex:ETHTOOL_OPTS="autoneg off speed 100 duplex full"
Note that changing speed or duplex settings almost always requires disabling autonegotiation with theautoneg offoption. This needs to be stated first, as the option entries are order dependent.GATEWAY=<address>, where <address> is the IP address of the network router or gateway device (if any).HWADDR=<MAC-address>, where <MAC-address> is the hardware address of the Ethernet device in the form AA:BB:CC:DD:EE:FF. This directive is useful for machines with multiple NICs to ensure that the interfaces are assigned the correct device names regardless of the configured load order for each NIC's module. This directive should not be used in conjunction withMACADDR.IPADDR=<address>, where<address>is the IP address.MACADDR=<MAC-address>, where <MAC-address> is the hardware address of the Ethernet device in the form AA:BB:CC:DD:EE:FF. This directive is used to assign a MAC address to an interface, overriding the one assigned to the physical NIC. This directive should not be used in conjunction withHWADDR.MASTER=<bond-interface>,where<bond-interface>is the channel bonding interface to which the interface the Ethernet interface is linked.This directive is used in conjunction with theSLAVEdirective.Refer to Section 8.2.3, “Channel Bonding Interfaces” for more about channel bonding interfaces.NETMASK=<mask>, where<mask>is the netmask value.NETWORK=<address>, where<address>is the network address. This directive is deprecated, as the value is calculated automatically withipcalc.ONBOOT=<answer>, where<answer>is one of the following:yes— This device should be activated at boot-time.no— This device should not be activated at boot-time.
PEERDNS=<answer>, where<answer>is one of the following:yes— Modify/etc/resolv.confif the DNS directive is set. If using DHCP, thenyesis the default.no— Do not modify/etc/resolv.conf.
SLAVE=<bond-interface>,where<bond-interface>is one of the following:yes— This device is controlled by the channel bonding interface specified in theMASTERdirective.no— This device is not controlled by the channel bonding interface specified in theMASTERdirective.
This directive is used in conjunction with theMASTERdirective.Refer to Section 8.2.3, “Channel Bonding Interfaces” for more about channel bond interfaces.SRCADDR=<address>, where<address>is the specified source IP address for outgoing packets.USERCTL=<answer>, where<answer>is one of the following:yes— Non-root users are allowed to control this device.no— Non-root users are not allowed to control this device.
