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2.2.5. Configuring a Wired (Ethernet) Connection

To configure a wired network connection, press the Super key to enter the Activities Overview, type control network and then press Enter. The Network settings tool appears.
Select the Wired connection from the left-hand-side menu if it is not already highlighted.
The system creates and configures a single wired connection profile called Wired by default. A profile is a collection of settings that is applied to an interface. More than one profile can be created for an interface and applied as needed. The default profile cannot be deleted but its settings can be changed. Although you can edit the default Wired profile by clicking the gear wheel icon, creating a new wired connection profile for your custom settings is recommended. You can create a new wired connection profile by clicking the Add Profile button.
When you add a new connection by clicking the Add Profile button, NetworkManager creates a new configuration file for that connection and then opens the same dialog that is used for editing an existing connection. The difference between these dialogs is that an existing connection profile has a Details and Reset menu entry. In effect, you are always editing a connection profile; the difference only lies in whether that connection previously existed or was just created by NetworkManager when you clicked Add Profile.

Configuring the Connection Name, Auto-Connect Behavior, and Availability Settings

Five settings in the Editing dialog are common to all connection types, see the General tab:

Configuring the Profile Identity

The final three configurable settings within the Identity dialog: the first below the name field is a text-entry field where you can specify a MAC (Media Access Control) address, and the second allows you to specify a cloned MAC address, and the third allows you to specify the MTU (Maximum Transmission Unit) value. Normally, you can leave the MAC address field blank and the MTU set to automatic. These defaults will suffice unless you are associating a wired connection with a second or specific NIC, or performing advanced networking. In such cases, see the following descriptions:
MAC Address
Network hardware such as a Network Interface Card (NIC) has a unique MAC address (Media Access Control; also known as a hardware address) that identifies it to the system. Running the ip addr command will show the MAC address associated with each interface. For example, in the following ip addr output, the MAC address for the eth0 interface (which is 52:54:00:26:9e:f1) immediately follows the link/ether keyword:
~]# ip addr
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 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 UNKNOWN qlen 1000
    link/ether 52:54:00:26:9e:f1 brd ff:ff:ff:ff:ff:ff
    inet brd scope global eth0
    inet6 fe80::5054:ff:fe26:9ef1/64 scope link
       valid_lft forever preferred_lft forever
A single system can have one or more NICs installed on it. The MAC address field therefore allows you to associate a specific NIC with a specific connection (or connections). As mentioned, you can determine the MAC address using the ip addr command, and then copy and paste that value into the MAC address text-entry field.
The cloned MAC address field is mostly for use in such situations were a network service has been restricted to a specific MAC address and you need to emulate that MAC address.
The MTU (Maximum Transmission Unit) value represents the size in bytes of the largest packet that the connection will use to transmit. This value defaults to 1500 when using IPv4, or a variable number 1280 or higher for IPv6, and does not generally need to be specified or changed.

Saving Your New (or Modified) Connection and Making Further Configurations

Once you have finished editing your wired connection, click the Apply button and NetworkManager will immediately save your customized configuration. Given a correct configuration, you can connect to your new or customized connection by selecting it from the network Notification Area applet. See Section 2.2.1, “Connecting to a Network Using a GUI” for information on using your new or altered connection.
You can further configure an existing connection by selecting it in the Network window and clicking gearwheel icon to return to the editing dialog.
Then, to configure: