If the NetworkManager service is running, you can use the nm-tool command to display a verbose listing of the state of the system's physical network interfaces, for example:

# nm-tool

NetworkManager Tool

State: connected

- Device: eth0  [System eth0] --------------------------------------------------
  Type:              Wired
  Driver:            e1000
  State:             connected
  Default:           yes
  HW Address:        08:00:27:16:C3:33

  Capabilities:
    Carrier Detect:  yes
    Speed:           1000 Mb/s

  Wired Properties
    Carrier:         on

  IPv4 Settings:
    Address:         10.0.2.15
    Prefix:          24 (255.255.255.0)
    Gateway:         10.0.2.2

    DNS:             192.168.249.52
    DNS:             192.168.249.41

You can also 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: eth0: <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 eth0
    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 eth0, specify its name as shown here:

# ip addr show dev eth0
2: eth0: <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 eth0
    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 eth1 interface and activates it:

# ip addr add 10.1.1.1/24 dev eth1
# ip link set eth1 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:

# service network restart
Shutting down interface eth0:  Device state: 3 (disconnected)
                                                           [  OK  ]
Shutting down loopback interface:                          [  OK  ]
Bringing up loopback interface:                            [  OK  ]
Bringing up interface eth0:  Active connection state: activating
Active connection path: /org/freedesktop/NetworkManager/ActiveConnection/1
state: activated
Connection activated
                                                           [  OK  ]

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 eth0
Device state: 3 (disconnected)
# ifup eth0
Active connection state: activating
Active connection path: /org/freedesktop/NetworkManager/ActiveConnection/1
state: activated
Connection activated

Alternatively, you can use the ip command:

# ip link set eth0 down
# ip link set eth0 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 nm-tool(1) manual pages.