How to Configure Network Interfaces using NMCLI on Centos 7.6

The first thing after installing a Linux OS as a server is configuring the network interface to have remote access and from your workstation/laptop and a cup of coffee you could manage your server at your convenient.

In this tutorial, we will use nmcli which stands for Network Manager Command Line tool for configuring our network interfaces.

Preliminary Note

The particularity of this command is you don’t need any requirements, however, it’s run as a root

The basic format of nmcli:

nmcli [OPTIONS] OBJECT { COMMAND | help }

OBJECT could be one of these options: connection, device, general, networking, radio, agent and monitor and we can use a prefix of these options: 

nmcli -p device --> nmcli -p dev --> nmcli -p d

Note: -p stands for --pretty is an option

In this part of the tutorial, we will cover two objects: Connection and Device

Network Device

We can use this object with those most used commands: status, show, and set

We will start with display our interfaces (devices) if we have many with there status:

nmcli device status

Output:

Network Device status

The first column is the name interfaces, my physical interface is ens33 it may be different from your environment, the last column is the name of profile it’s also called “connection profile”.

Another way:

nmcli -p device

The option -p stands for Pretty is a human-readable output.

Output :

Get list of network devices on CentOS

We use nmcli dev show to list all information about all interfaces (it’s a lot of information), so we will specify an interface we will use ens33:

nmcli dev show ens33

Output:

Show status of ens33 device

All information here is plenty explicit, we don’t need to go through this output.  

We could set any devices to be managed with nmcli or not, using the set command.

To list our devices and check if it’s managed or not.

nmcli device status

Output:

Use nmcli to show network device status

Notice the STATE column.

Now I will change ens33 to an unmanaged interface.

sudo nmcli device set ens33 managed no

Output:

Set network device status to unmanaged

Note that we can not manage ens33 interface with NetworkManager anymore but the device is still connected.

Let’s enable to manage ens33 interface:

sudo nmcli device set ens33 managed yes

Check the status of my interfaces:

nmcli device status

output :

Set device state to managed

Finally, we will see how to activate and deactivate our devices (interfaces) with disconnect and connect commands.

sudo nmcli dev disconnect ens33

You should have a successful message: Device “ens33” successfully disconnected.

Show the status of devices:

nmcli dev status

Output:

Device status

Notice the ens33 device is marked in red, the status is disconnected and no connexion profile attached. The device will be automatically activated after reboot or we can activate manually.

To activate our devices:

sudo nmcli dev connect ens33

Output:

Connect network device

The message with successful activation and a UUID of the profile connexion at the end.

Status of our interfaces:

nmcli dev status

Output:

Device connected successfully

The interface is no longer deactivate.

Profile Connection

Now let’s focus on the profile by showing the information:

nmcli connection show

Output:

Show connections

The first column is the name of the connection (not the device name), the second is The UUID or Universal Unique Identifier and the last one is the name of the device.

Profiles are the saved configuration of interfaces it’s stored in /etc/sysconfig/network-scripts/ and named with a prefix ifcfg- and then the name of the profile, let’s see:

Network scripts

The profiles with the name of devices are auto-generated, ifcfg-amine is created manually.

Now let’s create some profiles.

Note: I have two physical interfaces attached to my virtual machine ens33 and ens37.

We will create an ethernet configuration profile with a dynamic IP address.

sudo nmcli con add type ethernet con-name HomeDHCP ifname ens37

The interface is ethernet type, HomeDHCP is the name of the profile, ens37 is the interface which is the profile is attached to.

Output:

Add new ethernet profile

Let see profiles now:

Get list of profiles

Notice here the profile is created but not attached to ens37 interface, we have to activate our new profile by:

sudo nmcli con up HomeDHCP

Careful the name of the profile is case sensitive.

Output:

Activate connection

Let see again:

Result of activating the connection

Notice the first column NAME HomeDHCP is attached to ens37 interface. And ens37 profile (auto-generated) is not attached to any of the interfaces.

Let’s see inside the profile:

nmcli con show HomeDHCP

And check the file created in /etc/sysconfig/network-scripts/ifcfg-HomeDHCP

Content of network config script

Let’s deactivate the HomeDHCP profile from the ens37 interface.

sudo nmcli con down HomeDHCP

output :

New ens37 device is active

Notice that the default profile is attached to ens37 interface.

Let’s delete the HomeDHCP profile:

sudo nmcli con delete HomeDHCP

Output: 

Delete device

Result after deleting a device

No more HomeDHCP profile.

Let’s now create an ethernet configuration profile named HomeStatic with static address IP.

sudo nmcli con add type ethernet con-name HomeStatic ifname ens37 ip4 192.168.0.10/24 gw4 192.168.0.1

Output:

ethernet configuration profile

Check our interfaces connexion:

nmcli con s

Output:

New static IP device

Remember we have to attach the profile to the interface by activating the profile:

sudo nmcli con up HomeStatic

Output:

Connection activated successfully

Display the profile configuration:

nmcli dev show ens33

Output:

nmcli dev show ens33

Another way but there are many information so we will focus on what we want to see.

Output:

OutputOutput 2

Notice here we don’t have any information of DNS servers so we will add a dns server with another command:

sudo nmcli con modify HomeStatic ipv4.dns "8.8.8.8 8.8.4.4"

check :

nmcli c s HomeStatic

nmcli c s HomeStatic

Another way to add a dns server address:

sudo nmcli c mod HomeStatic +ipv4.dns "192.168.0.1"

sudo nmcli c mod HomeStatic +ipv4.dns "192.168.0.1"

And of course to delete a dns server address:

sudo nmcli c mod HomeStatic -ipv4.dns "192.168.0.1"

So far we go through the basic operations of networking to communicate with our servers with those two Objects and there commands in the next tutorial we will continue to explore and try to end up with a script to summarize what we have done.

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