In many administrative tasks, it is necessary to assign multiple IP addresses to a server—whether for proxy services, virtual hosting, or dedicated applications.
This article will guide you through correctly configuring additional IP addresses on Linux (Ubuntu, Debian, CentOS, RHEL, AlmaLinux, RockyLinux) and Windows Server 2022.

Temporary IP Assignment in Linux

To assign an IP address temporarily on Linux, run the following command:

IPv4

sudo ip addr add ADDITIONAL_IP dev INTERFACE

IPv6

sudo ip -6 addr add ADDITIONAL_IPV6/112 dev INTERFACE

Ubuntu/Debian

First, determine whether the old ifupdown system is in use:

dpkg -l | grep ii | awk '{print $2}' | grep ifupdown | wc -l

Returns 1 if ifupdown is installed, or 0 if not.

Check current network interfaces:

ip addr show

Output will list interfaces such as eth0, ens3, ens160.

Permanent Add via ifupdown

Open the configuration file:

sudo nano /etc/network/interfaces

Example configuration with an alias:

# Primary interface IPv4 + IPv6
auto eth0
iface eth0 inet static
    address YOUR_MAIN_IP
    netmask NETMASK
    gateway GATEWAY
    dns-nameservers DNS_1 DNS_2

iface eth0 inet6 static
    address YOUR_IPV6
    netmask 112
    gateway IPV6_GATEWAY
    dns-nameservers DNS6_1 DNS6_2

# Additional IPv4 (alias)
auto eth0:0
iface eth0:0 inet static
    address ADDITIONAL_IP
    netmask NETMASK

# Additional IPv6 (alias)
auto eth0:0
iface eth0:0 inet6 static
    address ADDITIONAL_IPV6
    netmask NETMASK

• eth0 — primary interface
• eth0:0 — alias interface for the extra IP

Apply changes:

sudo systemctl restart networking

Now the extra IP will persist after reboot.

Using Netplan

Netplan configs live in /etc/netplan/. Files must have a .yaml extension. List all desired addresses under your interface:

network:
    version: 2
    renderer: networkd
    ethernets:
        ens9:
            dhcp4: false
            addresses:
              - MAIN_IP       # Your primary IP
              - ADDITIONAL_IP # Additional IP

Test the new config (allows automatic rollback if you don’t confirm within 120s):

sudo netplan try

Or apply immediately (no rollback):

sudo netplan apply

CentOS/RHEL/AlmaLinux/RockyLinux

Determine which IP configuration method is active:

systemctl status NetworkManager

If it shows Active: active (running), NetworkManager is in use. Check its devices:

nmcli device status

To see if legacy scripts are used:

systemctl status network

NetworkManager

Permanent IPv4 add:

nmcli con mod INTERFACE +ipv4.addresses ADDITIONAL_IP
nmcli con up INTERFACE

Verify:

ip a

Network Scripts

cd /etc/sysconfig/network-scripts/
cp ifcfg-eth0 ifcfg-eth0:0

Edit ifcfg-eth0:0:

DEVICE=eth0:0
BOOTPROTO=static
ONBOOT=yes
IPADDR=ADDITIONAL_IP
NETMASK=NETMASK

systemctl restart network

ifdown eth0:0 ; ifup eth0:0

Windows Server

List IPv4 addresses in PowerShell:

Get-NetIPAddress | Where-Object {$_.AddressFamily -eq "IPv4"}

List adapters:

Get-NetAdapter

PowerShell Add

New-NetIPAddress -InterfaceAlias "INTERFACE_ALIAS" -IPAddress "ADDITIONAL_IP" -PrefixLength 32 -DefaultGateway "GATEWAY_IP"

Verify:

Get-NetIPAddress -InterfaceAlias "INTERFACE_ALIAS"

GUI Method

1. Open Start → Settings → Network & Internet

2. Under Status, click Change adapter options

3. Right-click the adapter → Properties

4. Select IPv4 → Properties → Advanced…

5. Click Add…

6. Enter the extra IP and subnet mask → Add

Verification

Linux:

ping -c 4 ADDITIONAL_IP

Windows:

ping ADDITIONAL_IP

If the IP responds to ping, the configuration is correct.