How to configure IP aliasing

Debian 12, Ubuntu 22.04 and following

The configuration file for your Additional IP addresses is located in the folder /etc/netplan/. In this example it is called 50-cloud-init.yaml.

The best practice approach is to create a separate configuration file to set up Additional IP addresses. This way, you can easily revert the changes in case of an error.

Step 1: Create the network configuration file

In our example, our file is called 51-cloud-init.yaml:

sudo touch /etc/netplan/51-cloud-init.yaml

Step 2: Edit the configuration file

You can verify your network interface name with this command:

ip a

Next, open the network configuration file for editing with the following command:

sudo nano /etc/netplan/51-cloud-init.yaml

Edit the file with the content below, replacing INTERFACE_NAME and ADDITIONAL_IP with your own values:

network:
   version: 2
   ethernets:
       INTERFACE_NAME:
           dhcp4: true
           addresses:
           - ADDITIONAL_IP/32

If you have more Additional IPs to configure, the configuration file should look like this:

network:
   version: 2
   ethernets:
       INTERFACE_NAME:
           dhcp4: true
           addresses:
           - ADDITIONAL_IP1/32
           - ADDITIONAL_IP2/32

network:
   version: 2
   ethernets:
       eth0:
           dhcp4: true
           addresses:
           - 203.0.113.0/32

Save and close the file.

Step 3: Apply the new network configuration

You can test your configuration using this command:

sudo netplan try

If it is correct, apply it using the following command:

sudo netplan apply

AlmaLinux (8/9), Rocky Linux (8/9)

The main configuration file is located in /etc/sysconfig/network-scripts/. In this example it is called ifcfg-eth0. Before making changes, verify the actual file name in this folder.

For each Additional IP to be configured, we create a separate configuration file with the following parameters: ifcfg-NETWORK_INTERFACE:ID. Where NETWORK_INTERFACE is the physical interface and ID is the virtual network interface or ethernet alias starting with a value of 0. For example, for our interface named eth0 the first alias is eth0:0, the second alias is eth0:1, etc...

Step 1: Determine the interface

ip a

Step 2: Create the configuration file

First, create the configuration file. Replace NETWORK_INTERFACE:ID with your own values.

sudo nano /etc/sysconfig/network-scripts/ifcfg-NETWORK_INTERFACE:ID

Next, edit the file with the content below, replacing NETWORK_INTERFACE:ID, and ADDITIONAL_IP with your own values:

DEVICE=NETWORK_INTERFACE:ID
ONBOOT=yes
BOOTPROTO=none # For CentOS use "static"
IPADDR=ADDITIONAL_IP
NETMASK=255.255.255.255
BROADCAST=ADDITIONAL_IP

DEVICE=eth0:0
ONBOOT=yes
BOOTPROTO=none # For CentOS use "static"
IPADDR=203.0.113.0
NETMASK=255.255.255.255
BROADCAST=203.0.113.0

Step 3: Restart the interface

sudo systemctl restart NetworkManager

CentOS

sudo systemctl restart network

Fedora 42, AlmaLinux & Rocky Linux (10)

Fedora now uses keyfiles. NetworkManager previously stored network profiles in ifcfg format in this directory: /etc/sysconfig/network-scripts/. However, the ifcfg format is now deprecated. By default, NetworkManager no longer creates new profiles in this format. The configuration file is now found in /etc/NetworkManager/system-connections/.

Step 1: Create a backup

In our example, our file is called cloud-init-eno1.nmconnection, so we make a copy of the cloud-init-eno1.nmconnection file using the following command:

sudo cp -r /etc/NetworkManager/system-connections/cloud-init-eno1.nmconnection /etc/NetworkManager/system-connections/cloud-init-eno1.nmconnection.bak

In case of a mistake, you will be able to revert the changes, using the commands below:

sudo rm -f /etc/NetworkManager/system-connections/cloud-init-eno1.nmconnection
sudo cp /etc/NetworkManager/system-connections/cloud-init-eno1.nmconnection.bak /etc/NetworkManager/system-connections/cloud-init-eno1.nmconnection

Step 2: Edit the config file

sudo nano /etc/NetworkManager/system-connections/cloud-init-eno1.nmconnection

Do not modify the existing lines in the configuration file, add your Additional IP to the file as follows, replacing ADDITIONAL_IP/32 with your own values:

[ipv4]
method=auto
may-fail=false
address1=ADDITIONAL_IP/32

If you have two Additional IPs to configure, the configuration should look like this:

[ipv4]
method=auto
may-fail=false
address1=ADDITIONAL_IP1/32
address2=ADDITIONAL_IP2/32

[ipv4]
method=auto
may-fail=false
address1=203.0.113.0/32

Step 3: Restart the interface

You now need to restart your interface:

sudo systemctl restart NetworkManager

cPanel

Step 1: Access the WHM IP management section

In the WHM control panel, click on IP Functions and select Add a New IP Address in the left-hand sidebar.

Step 2: Add the Additional IP information

Enter your Additional IP in the form xxx.xxx.xxx.xxx into the field “New IP or IP range to add”.

Select 255.255.255.255 as your subnet mask, then click on Submit.

Step 3: Check the current IP configuration

Back in the section IP Functions, click on Show or Delete Current IP Addresses to verify that the Additional IP address was added correctly.

Plesk

Step 1: Access the Plesk IP management section

In the Plesk control panel, choose Tools & Settings from the left-hand sidebar.

Click on IP Addresses under Tools & Resources.

Step 2: Add the additional IP information

In this section, click on the button Add IP Address.

Enter your Additional IP in the form xxx.xxx.xxx.xxx/32 into the field "IP address and subnet mask", then click on OK.

Step 3: Check the current IP configuration

Back in the section "IP Addresses", verify that the Additional IP address was added correctly.

Windows Servers

Step 1: Verify the network configuration

Right-click on the Start Menu button and open Run.

Type cmd and click OK to open the command line application.

To retrieve the current IP configuration, enter ipconfig at the command prompt.

C:\Users\Administrator>ipconfig

Windows IP Configuration

Ethernet adapter Ethernet:

   Connection-specific DNS Suffix  . : openstacklocal
   Link-local IPv6 Address . . . . . : fe90::30gf:258a:84d6:abcf%5
   IPv4 Address. . . . . . . . . . . : 192.0.2.29
   Subnet Mask . . . . . . . . . . . : 255.255.255.255
   Default Gateway . . . . . . . . . : 192.0.2.1

Step 2: Change the IPv4 Properties

Now you need to change the IP properties to a static configuration.

1. Go to Start > Control Panel > Network and Internet > Network and Sharing Centre > Change Adapter Settings (in the left-hand menu).
2. Right-click on Ethernet.
3. Click on Properties.
4. Select Internet Protocol Version 4 (TCP/IPv4), then click on Properties.
5. Click on Use the following IP address and type in your server’s primary IP, subnet mask and default gateway information obtained by using the ipconfig command above. In the "Preferred DNS Server" box, type 213.186.33.99.

Once done, click on Advanced.

Step 3: Add the Additional IP in the "Advanced TCP/IP Settings"

In the new window, click on Add... under "IP addresses". Enter your Additional IP address and the subnet mask (255.255.255.255).

Confirm by clicking on Add.

Once done, click on OK to apply the configuration.

You will lose the connection to the server for a few seconds.

Step 4: Check the new network configuration

Open the command prompt (cmd) and enter ipconfig. The configuration should now include the new Additional IP address.

C:\Users\Administrator>ipconfig

Windows IP Configuration

Ethernet adapter Ethernet:

   Connection-specific DNS Suffix  . :
   Link-local IPv6 Address . . . . . : fe90::30gf:258a:84d6:abcf%5
   IPv4 Address. . . . . . . . . . . : 192.0.2.29
   Subnet Mask . . . . . . . . . . . : 255.255.255.255
   IPv4 Address. . . . . . . . . . . : 203.0.113.0
   Subnet Mask . . . . . . . . . . . : 255.255.255.255
   Default Gateway . . . . . . . . . : 192.0.2.1