Configuring IP aliasing

Fedora 42 and following, 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

First, make a copy of the configuration file, so that you can revert at any time. In our example, our configuration file is called cloud-init-eno1.nmconnection.

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

Step 2: Edit the config file

To obtain the name of your network interface in order to edit the appropriate network file, you can run one of the following commands:

ip a

nmcli connection show

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

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

[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=203.0.113.1/32

Step 3: Restart the interface

You now need to restart your interface:

sudo systemctl restart NetworkManager

Debian 12, Ubuntu 20.04 and following

By default, the configuration files are located in the /etc/netplan directory.

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: Determine the interface

ip a

Note the name of the interface (the one on which your server's main IP address is configured).

Step 2: Create and edit the configuration file

Next, create a configuration file with a .yaml extension. In our example, our file is called 51-cloud-init.yaml.

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 two 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:
           - 203.0.113.1/32 

Save and close the file. You can test the configuration with the following command:

sudo netplan try

Step 3: Apply the change

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 seperate 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

Note the name of the interface (the one on which your server's main IP address is configured).

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=203.0.113.1
NETMASK=255.255.255.255
BROADCAST=203.0.113.1

Step 3: Restart the interface

Next, restart the network interface with the following command:

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.

Windows Servers

Windows servers are often DHCP-enabled in the network configuration. If you have already set up an Additional IP or switched your configuration to a fixed IP, go directly to the next step.

Otherwise, you need to first switch from a network-level DHCP configuration to a fixed IP configuration.

Open the command prompt cmd or powershell, then type the following command:

ipconfig

This will return a result similar to the following example:

Identify and write down your IPv4, subnet mask, default gateway and the name of the network interface controller (network adapter).

In our example, the server IP is 192.0.2.28.

You can perform the next steps via either a command-line interface or the graphical user interface.

Via a command-line interface (recommended)

In the commands below, you need to replace:

In the command prompt:

1. Switch to a fixed IP

netsh interface ipv4 set address name="NETWORK_ADAPTER" static IP_ADDRESS SUBNET_MASK GATEWAY

2. Set the DNS server

netsh interface ipv4 set dns name="NETWORK_ADAPTER" static 213.186.33.99

3. Add an Additional IP

netsh interface ipv4 add address "NETWORK_ADAPTER" ADDITIONAL_IP 255.255.255.255

Your Additional IP is now functional.

ipconfig

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.