Configuring IP aliasing

Last updated 30th November 2021

Objective

IP aliasing refers to a special network configuration for certain OVHcloud services. Failover IPs allow you to associate multiple IP addresses with a single network interface.

This guide explains how to add failover IP addresses to your network configuration.

Requirements

• A Virtual Private Server in your OVHcloud account
• A failover IP address or a failover IP block
• Administrative access (root) via SSH or GUI to your server
• Basic networking and administration knowledge

Instructions

The following sections contain the configurations for the most commonly used distributions/operating systems. The first step is always to log in to your server via SSH or a GUI login session (RDP for a Windows VPS). The examples below presume you are logged in as a user with elevated permissions (Administrator/sudo).

Please take note of the following terminology that will be used in code examples and instructions of the guide sections below:

Debian 10/11

Step 1: Disable automatic network configuration

Open the following file path with a text editor:

sudo nano /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg

Enter the following line, then save and exit the editor.

network: {config: disabled}

Creating this configuration file will prevent changes to your network configuration from being made automatically.

Step 2: Edit the network configuration file

You can verify your network interface name with this command:

ip a

Open the network configuration file for editing with the following command:

sudo nano /etc/network/interfaces.d/50-cloud-init

Then add the following lines:

auto NETWORK_INTERFACE:ID
iface NETWORK_INTERFACE:ID inet static
address IP_FAILOVER
netmask 255.255.255.255

Step 3: Restart the interface

Apply the changes with the following command:

sudo systemctl restart networking

Ubuntu 20.04

The configuration file for your failover IP addresses is located in /etc/netplan/. In this example it is called "50-cloud-init.yaml". Before making changes, verify the actual file name in this folder. Each failover IP address will need its own line within the file.

Step 1: Disable automatic network configuration

Open the following file path with a text editor:

sudo nano /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg

Enter the following line, then save and exit the editor.

network: {config: disabled}

Creating this configuration file will prevent changes to your network configuration from being made automatically.

Step 2: Edit the configuration file

You can verify your network interface name with this command:

ip a

Open the network configuration file for editing with the following command:

sudo nano /etc/netplan/50-cloud-init.yaml

Do not modify the existing lines in the configuration file. Add your failover IP address by adding a second configuration block for the public interface according to the example below:

network:
    version: 2
    ethernets:
        NETWORK_INTERFACE:
            dhcp4: true
            match:
                macaddress: fa:xx:xx:xx:xx:63
            set-name: NETWORK_INTERFACE            
        NETWORK_INTERFACE:
            dhcp4: true
            match:
                macaddress: fa:xx:xx:xx:xx:63
            set-name: NETWORK_INTERFACE
            addresses:
            - IP_FAILOVER/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

Repeat this procedure for each failover IP address.

Windows Server 2016

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.

In order to retrieve the current IP configuration, enter ipconfig at the command prompt.

Step 2: Change the IPv4 Properties

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

Open the adapter settings in the Windows control panel and then open the Properties of Internet Protocol Version 4 (TCP/IPv4).

In the IPv4 Properties window, select Use the following IP address. Enter the IP address which you have retrieved in the first step, then click on Advanced.

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

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

Confirm by clicking on Add.

Step 4: Restart the network interface

Back in the control panel (Network Connections), right-click on your network interface and then select Disable.

To restart it, right-click on it again and then select Enable.

Step 5: Check the new network configuration

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

cPanel (CentOS 7) / Red Hat derivatives

Step 1: Edit the network configuration file

You can verify your network interface name with this command:

ip a

Open the network configuration file for editing:

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

Then add these lines:

DEVICE=NETWORK_INTERFACE:ID
BOOTPROTO=static
IPADDR=IP_FAILOVER
NETMASK=255.255.255.255
BROADCAST=IP_FAILOVER
ONBOOT=yes

Step 2: Restart the interface

Apply the changes with the following command:

sudo systemctl restart networking

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 failover 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 failover IP address was added correctly.

Troubleshooting

First, restart your server from the command line or its GUI. If you are still unable to establish a connection from the public network to your alias IP and suspect a network problem, you need to reboot the server in rescue mode. Then you can set up the failover IP address directly on the server.

Once you are connected to your server via SSH, enter the following command:

ifconfig ens3:0 IP_FAILOVER netmask 255.255.255.255 broadcast IP_FAILOVER up

To test the connection, simply ping your failover IP from the outside. If it responds in rescue mode, that probably means that there is a configuration error. If, however, the IP is still not working, please inform our support teams by creating a support request in your OVHcloud Control Panel for further investigations.

Go further

Activating Rescue Mode on VPS

Join our community of users on https://community.ovh.com/en/.

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