10.1 About Network Interfaces

Each physical and virtual network device on an Oracle Linux system has an associated configuration file named ifcfg-interface in the /etc/sysconfig/network-scripts directory, where interface is the name of the interface. For example:

# cd /etc/sysconfig/network-scripts
# ls ifcfg-*
ifcfg-em1  ifcfg-em2  ifcfg-lo

In this example, there are two configuration files for motherboard-based Ethernet interfaces, ifcfg-em1 and ifcfg-em2, and one for the loopback interface, ifcfg-lo. The system reads the configuration files at boot time to configure the network interfaces.

On your system, you might see other names for network interfaces. See Section 10.2, “About Network Interface Names”.

The following are sample entries from an ifcfg-em1 file for a network interface that obtains its IP address using the Dynamic Host Configuration Protocol (DHCP):

DEVICE="em1"
NM_CONTROLLED="yes"
ONBOOT=yes
USERCTL=no
TYPE=Ethernet
BOOTPROTO=dhcp
DEFROUTE=yes
IPV4_FAILURE_FATAL=yes
IPV6INIT=no
NAME="System em1"
UUID=5fb06bd0-0bb0-7ffb-45f1-d6edd65f3e03
HWADDR=08:00:27:16:C3:33
PEERDNS=yes
PEERROUTES=yes

If the interface is configured with a static IP address, the file contains entries such as the following:

DEVICE="em1"
NM_CONTROLLED="yes"
ONBOOT=yes
USERCTL=no
TYPE=Ethernet
BOOTPROTO=none
DEFROUTE=yes
IPV4_FAILURE_FATAL=yes
IPV6INIT=no
NAME="System em1"
UUID=5fb06bd0-0bb0-7ffb-45f1-d6edd65f3e03
HWADDR=08:00:27:16:C3:33
IPADDR=192.168.1.101
NETMASK=255.255.255.0
BROADCAST=192.168.1.255
PEERDNS=yes
PEERROUTES=yes

The following configuration parameters are typically used in interface configuration files:

BOOTPROTO

How the interface obtains its IP address:

bootp

Bootstrap Protocol (BOOTP).

dhcp

Dynamic Host Configuration Protocol (DHCP).

none

Statically configured IP address.

BROADCAST

IPv4 broadcast address.

DEFROUTE

Whether this interface is the default route.

DEVICE

Name of the physical network interface device (or a PPP logical device).

GATEWAYN

IPv4 gateway address for the interface. As an interface can be associated with several combinations of IP address, network mask prefix length, and gateway address, these are numbered starting from 0.

HWADDR

Media access control (MAC) address of an Ethernet device.

IPADDRN

IPv4 address of the interface.

IPV4_FAILURE_FATAL

Whether the device is disabled if IPv4 configuration fails.

IPV6_DEFAULTGW

IPv6 gateway address for the interface. For example: IPV6_DEFAULTGW=2001:0daa::2%em1.

IPV6_FAILURE_FATAL

Whether the device is disabled if IPv6 configuration fails.

IPV6ADDR

IPv6 address of the interface in CIDR notation, including the network mask prefix length. For example: IPV6ADDR="2001:0db8:1e11:115b::1/32"

IPV6INIT

Whether to enable IPv6 for the interface.

MASTER

Specifies the name of the master bonded interface, of which this interface is slave.

NAME

Name of the interface as displayed in the Network Connections GUI.

NETWORK

IPV4 address of the network.

NM_CONTROLLED

Whether the network interface device is controlled by the network management daemon, NetworkManager.

ONBOOT

Whether the interface is activated at boot time.

PEERDNS

Whether the /etc/resolv.conf file used for DNS resolution contains information obtained from the DHCP server.

PEERROUTES

Whether the information for the routing table entry that defines the default gateway for the interface is obtained from the DHCP server.

PREFIXN

Length of the IPv4 network mask prefix for the interface.

SLAVE

Specifies that this interface is a component of a bonded interface.

TYPE

Interface type.

USERCTL

Whether users other than root can control the state of this interface.

UUID

Universally unique identifier for the network interface device.