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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 1.2, “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:

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:

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:

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
(ethN and
wlanN) 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:

# 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:

# 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:

# 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:

# ip addr add 10.1.1.1/24 dev em2
# 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:

# 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:

# ifdown em1
# 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:

# ip link set em1 down
# 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:

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:

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.

# teamdctl team0 port add em5

# teamdctl team0 port remove em5

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

# teamd -t team0 -k

# 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

# teamnl team0 ports
 5: em4: up 1000Mbit FD 
 4: em3: up 1000Mbit FD 

# 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

# 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:

# 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:

# 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.

# 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:

# systemctl restart network

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

# 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:

# ip route del default
# ip route show
10.0.2.0/24 dev em1  proto kernel  scope link  src 10.0.2.15 
# ip ro add default via 10.0.2.1 dev em1 proto static
# 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:

# ip route add 10.0.4.0/24 via 10.0.2.1 dev em2
# 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 
# ip route del 10.0.3.0/24
# 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:

# 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.