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 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).

GATEWAY N

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.

IPADDR N

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 primary bonded interface, of which this interface is backup.

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.

PREFIX N

Length of the IPv4 network mask prefix for the interface.

SLAVE

Specifies that this interface is a backup 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.

Network interface names are based on information derived from the system BIOS or alternatively from a device's firmware, system path, or MAC address. This feature ensures that interface names persist across system reboots, hardware reconfiguration, and updates to device drivers and the kernel.

If you enable the biosdevname boot option (biosdevname=1), the biosdevname plugin to the udev device manager assigns names to network interfaces as follows:

• Ethernet interfaces on the motherboard are named em N, where N is the number of the interface starting from 1.

• Network interfaces on a PCI card are named p S p P, where S is the slot number and P is the port number.

• Virtual interfaces are named p S p P _ V, where S is the slot number, P is the port number, and V is the virtual interface number.

If biosdevname is set to 0 (the default), systemd naming assigns the prefixes, en, wl, and ww to Ethernet, wireless LAN, and wireless WAN interfaces respectively. The prefix is followed by a suffix based on the hardware configuration, system bus configuration, or MAC address of the device:

o N

Onboard device with index number N.

pBsS[fF][dD]

PCI device with bus number B, slot number S, function number F, and device ID D.

pBsS[fF][uP]...[cC][iI]

USB device with bus number B, slot number S, function number F, port number P, configuration number C, and interface number I.

sS[fF][dD]

Hot-plug device with slot number S, function number F, and device ID D.

x M

Device with MAC address M.

For example, an Ethernet port on the motherboard might be named eno1 or em1, depending on whether the value of biosdevname is 0 or 1.

The kernel assigns a legacy, unpredictable network interface name (eth N and wlan N) only if it cannot discover any information about the device that would allow it to disambiguate the device from other such devices. You can use the net.ifnames=0 boot parameter to reinstate the legacy naming scheme.

The following sections describe additional network configuration files that you might need to configure on a system.

127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6

hosts:      files dns nisplus

search us.mydomain.com mydomain.com
nameserver 192.168.154.3
nameserver 192.168.154.4
nameserver 10.216.106.3

NETWORKING=yes
NETWORKING_IPV6=no
HOSTNAME=host20.mydomain.com
GATEWAY=192.168.1.1

If the NetworkManager service is running, you can use the nmcli command to display the state of the system's physical network interfaces, for example:

sudo nmcli device status

DEVICE  TYPE      STATE       
em1     ethernet  connected   
em2     ethernet  connected   
lo      loopback  unmanaged

You can use the ip command to display the status of an interface, for debugging, or for system tuning. For example, to display the status of all active interfaces:

sudo ip addr show

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: em1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 08:00:27:16:c3:33 brd ff:ff:ff:ff:ff:ff
    inet 10.0.2.15/24 brd 10.0.2.255 scope global em1
    inet6 fe80::a00:27ff:fe16:c333/64 scope link 
       valid_lft forever preferred_lft forever

For each network interface, the output shows the current IP address, and the status of the interface. To display the status of a single interface such as em1, specify its name as shown here:

sudo ip addr show dev em1

2: em1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 08:00:27:16:c3:33 brd ff:ff:ff:ff:ff:ff
    inet 10.0.2.15/24 brd 10.0.2.255 scope global em1
    inet6 fe80::a00:27ff:fe16:c333/64 scope link 
       valid_lft forever preferred_lft forever

You can also use ip to set properties and activate a network interface. The following example sets the IP address of the em2 interface and activates it:

sudo ip addr add 10.1.1.1/24 dev em2
sudo ip link set em2 up

Any settings that you configure for network interfaces using ip do not persist across system reboots. To make the changes permanent, set the properties in the /etc/sysconfig/network-scripts/ifcfg-interface file.

Any changes that you make to an interface file in /etc/sysconfig/network-scripts do not take effect until you restart the network service or bring the interface down and back up again. For example, to restart the network service:

sudo systemctl restart network

To restart an individual interface, you can use the ifup or ifdown commands, which invoke the script in /etc/sysconfig/network-scripts that corresponds to the interface type, for example:

sudo ifdown em1
sudo ifup em1

Connection successfully activated 
(D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/5)

Alternatively, you can use the ip command to stop and start network activity on an interface without completely tearing down and rebuilding its configuration:

sudo ip link set em1 down
sudo ip link set em1 up

The ethtool utility is useful for diagnosing potentially mismatched settings that affect performance, and allows you to query and set the low-level properties of a network device. Any changes that you make using ethtool do not persist across a reboot. To make the changes permanent, modify the settings in the device's ifcfg-interface file in /etc/sysconfig/network-scripts.

For more information, see the ethtool(8), ifup(8), ip(8), and nmcli(1) manual pages.

The NetworkManager service dynamically detects and configures network connections. You can click on the network icon in the GNOME notification area to obtain information about the status of the network interfaces and to manage network connections:

• To enable or disable a network interface from the pull-down menu, use the On/Off toggle.

• To display the Settings window, select Network Settings from the drop-down menu.

Figure 1-2 shows the Network Settings editor.

To edit an existing interface, select it from the list and click the gear icon. You can add a profile to any interface to provide alternate configurations that you can use at any point in time. You can equally use this window to configure a network proxy or add an enable a Virtual Private Network (VPN) connection.

To perform more complex configuration and to add additional connection types, use the Network Connections editor. This tool allows you to configure wired, wireless, mobile broadband, VPN, Digital Subscriber Link (DSL), and virtual (bond, bridge, team, and VLAN) interfaces. You can open this window by using the nm-connection-editor command. Figure 1-2 shows the Network Connections editor.

To create a new network interface, click the + icon, select the type of interface (hardware, virtual, or VPN) and click Create. To edit an existing interface, select it from the list and click the gear icon. To remove a selected interface, click the - icon.

You can also use the nmcli command to manage network connections through NetworkManager. For more information, see the nmcli(1) manual page.

Network interface bonding combines multiple network connections into a single logical interface. A bonded network interface can increase data throughput by load balancing or can provide redundancy by allowing failover from one component device to another. By default, a bonded interface appears like a normal network device to the kernel, but it sends out network packets over the available secondary devices by using a simple round-robin scheduler. You can configure bonding module parameters in the bonded interface's configuration file to alter the behavior of load-balancing and device failover.

Basic load-balancing modes (balance-rr and balance-xor) work with any switch that supports EtherChannel or trunking. Advanced load-balancing modes (balance-tlb and balance-alb) do not impose requirements on the switching hardware, but do require that the device driver for each component interfaces implement certain specific features such as support for ethtool or the ability to modify the hardware address while the device is active. For more information see /usr/share/doc/iputils-*/README.bonding.

Network interface teaming is similar to network interface bonding and provides a way of implementing link aggregation that is relatively maintenance-free, as well as being simpler to modify, expand, and debug as compared with bonding.

A lightweight kernel driver implements teaming and the teamd daemon implements load-balancing and failover schemes termed runners. The following standard runners are defined:

activebackup

Monitors the link for changes and selects the active port that is used to send packets.

broadcast

Sends packets on all member ports.

lacp

Provides load balancing by implementing the Link Aggregation Control Protocol 802.3ad on the member ports.

loadbalance

In passive mode, uses the BPF hash function to select the port that is used to send packets.

In active mode, uses a balancing algorithm to distribute outgoing packets over the available ports.

random

Selects a port at random to send each outgoing packet.

Note:

UEK R3 does not currently support this runner mode.

roundrobin

Transmits packets over the available ports in a round-robin fashion.

For specialized applications, you can create customized runners that teamd can interpret. The teamdctl command allows you to control the operation of teamd.

For more information, see the teamd.conf(5) manual page.

sudo teamdctl team0 port add em5

sudo teamdctl team0 port remove em5

sudo teamdctl team0 port config update em3 '{"prio": -10, "sticky": false}'

# teamd -t team0 -k

sudo ip addr show dev team0

7: team0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP 
    link/ether 08:00:27:15:7a:f1 brd ff:ff:ff:ff:ff:ff
    inet 10.0.0.5/24 scope global team0
       valid_lft forever preferred_lft forever
    inet6 fe80::a00:27ff:fe15:7af1/64 scope link 
       valid_lft forever preferred_lft forever

sudo teamnl team0 ports

 5: em4: up 1000Mbit FD 
 4: em3: up 1000Mbit FD 

sudo teamdctl team0 state

setup:
  runner: activebackup
ports:
  em3
    link watches:
      link summary: down
      instance[link_watch_0]:
        name: ethtool
        link: down
  em4
    link watches:
      link summary: up
      instance[link_watch_0]:
        name: ethtool
        link: up
runner:
  active port: em4

sudo teamdctl team0 config dump

{
    "device": "team0",
    "link_watch": {
        "name": "ethtool"
    },
    "mcast_rejoin": {
        "count": 1
    },
    "notify_peers": {
        "count": 1
    },
    "ports": {
        "em3": {
            "prio": -10,
            "sticky": true
        },
        "em4": {
            "prio": 100
        }
    },
    "runner": {
        "name": "activebackup"
    }
}

A virtual local area network (VLAN) consists of a group of machines that can communicate as if they were attached to the same physical network. A VLAN allows you to group systems regardless of their actual physical location on a LAN. In a VLAN that uses untagged data frames, you create the broadcast domain by assigning the ports of network switches to the same permanent VLAN ID or PVID (other than 1, which is the default VLAN). All ports that you assign with this PVID are in a single broadcast domain. Broadcasts between devices in the same VLAN are not visible to other ports with a different VLAN, even if they exist on the same switch.

You can use the Network Settings editor or the nmcli command to create a VLAN device for an Ethernet interface.

To create a VLAN device from the command line, enter:

sudo nmcli con add type vlan con-name bond0-pvid10 ifname bond0-pvid10 dev bond0 id 10

This example sets up the VLAN device bond0-pvid10 with a PVID of 10 for the bonded interface bond0. In addition to the regular interface, bond0, which uses the physical LAN, you now have a VLAN device, bond0-pvid10, which can use untagged frames to access the virtual LAN.

You can also use the command to set up a VLAN device for a non-bonded interface, for example:

sudo nmcli con add type vlan con-name em1-pvid5 ifname em1-pvid5 dev em1 id 5

To obtain information about the configured VLAN interfaces, view the files in the /proc/net/vlan directory.

sudo ip link add link em1 name em1.5 type vlan id 5

A system uses its routing table to determine which network interface to use when sending packets to remote systems. If a system has only a single interface, it is sufficient to configure the IP address of a gateway system on the local network that routes packets to other networks.

To create a default route for IPv4 network packets, include an entry for GATEWAY in the /etc/sysconfig/network file. For example, the following entry configures the IP address of the gateway system:

GATEWAY=192.0.2.1

If your system has more than one network interface, you can specify which interface should be used:

GATEWAY=192.0.2.1
GATEWAYDEV=em1

A single statement is usually sufficient to define the gateway for IPv6 packets, for example:

IPV6_DEFAULTGW="2001:db8:1e10:115b::2%em1"

Any changes that you make to /etc/sysconfig/network do not take effect until you restart the network service:

sudo systemctl restart network

To display the routing table, use the ip route show command, for example:

sudo ip route show

10.0.2.0/24 dev em1  proto kernel  scope link  src 10.0.2.15 
default via 10.0.2.2 dev em1  proto static 

This example shows that packets destined for the local network (10.0.2.0/24) do not use the gateway. The default entry means that any packets destined for addresses outside the local network are routed via the gateway 10.0.2.2.

You can also use the netstat -rn command to display this information:

Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
10.0.2.0        0.0.0.0         255.255.255.0   U         0 0          0 em1
0.0.0.0         10.0.2.2        0.0.0.0         UG        0 0          0 em1

To add or delete a route from the table, use the ip route add or ip route del commands. For example, to replace the entry for the static default route:

sudo ip route del default
sudo ip route show

10.0.2.0/24 dev em1  proto kernel  scope link  src 10.0.2.15

sudo ip ro add default via 10.0.2.1 dev em1 proto static
sudo ip route show

10.0.2.0/24 dev em1  proto kernel  scope link  src 10.0.2.15  
default via 10.0.2.1 dev em1  proto static 

To add a route to the network 10.0.3.0/24 via 10.0.3.1 over interface em2, and then delete that route:

sudo ip route add 10.0.4.0/24 via 10.0.2.1 dev em2
sudo ip route show

10.0.2.0/24 dev em1  proto kernel  scope link  src 10.0.2.15 
10.0.3.0/24 via 10.0.3.1 dev em2
default via 10.0.2.2 dev em1  proto static

sudo ip route del 10.0.3.0/24
sudo ip route show

10.0.2.0/24 dev em1  proto kernel  scope link  src 10.0.2.15 
default via 10.0.2.2 dev em1  proto static 

The ip route get command is a useful feature that allows you to query the route on which the system will send packets to reach a specified IP address, for example:

sudo ip route get 23.6.118.140

23.6.118.140 via 10.0.2.2 dev em1  src 10.0.2.15 
    cache  mtu 1500 advmss 1460 hoplimit 64

In this example, packets to 23.6.118.140 are sent out of the em1 interface via the gateway 10.0.2.2.

Any changes that you make to the routing table using ip route do not persist across system reboots. To permanently configure static routes, you can configure them by creating a route-interface file in/etc/sysconfig/network-scripts for the interface. For example, you would configure a static route for the em1 interface in a file named route-em1. An entry in these files can take the same format as the arguments to the ip route add command.

For example, to define a default gateway entry for em1, create an entry such as the following in route-em1:

default via 10.0.2.1 dev em1

The following entry in route-em2 would define a route to 10.0.3.0/24 via 10.0.3.1 over em2:

10.0.3.0/24 via 10.0.3.1 dev em2

Any changes that you make to a route-interface file do not take effect until you restart either the network service or the interface.

For more information, see the ip(8) and netstat(8) manual pages.