Assign Multiple Secondary IPs on Different Operating Systems

This guide explains how to add multiple secondary IP addresses on your network interface across Ubuntu/Debian, CentOS/AlmaLinux.

---

🐧 Ubuntu / Debian

1. Check active interface

ip a

Example output:

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 ...
    inet 192.168.1.100/24 brd 192.168.1.255 scope global eth0

Interface name here is eth0.

2. Backup network configuration

sudo cp /etc/netplan/50-cloud-init.yaml /etc/netplan/50-cloud-init.yaml.bak

(Optional: Backup the full Netplan directory)

sudo cp -r /etc/netplan /etc/netplan_backup_$(date +%F)

3. Edit configuration

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

Add multiple IPs under your interface:

network:
  version: 2
  ethernets:
    eth0:
      dhcp4: no
      addresses:
        - 192.168.1.100/24   # Primary
        - 192.168.1.101/24   # Secondary 1
        - 192.168.1.102/24   # Secondary 2
      gateway4: 192.168.1.1
      nameservers:
        addresses:
          - 8.8.8.8
          - 8.8.4.4

4. Apply and verify

sudo netplan apply
ip a show eth0

---

🐧 CentOS / AlmaLinux / Rocky

1. Check active interface

ip addr

Example output:

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> ...
    inet 192.168.1.100/24 brd 192.168.1.255 scope global eth0

Interface name here is eth0.

2. Backup existing config

sudo cp /etc/sysconfig/network-scripts/ifcfg-eth0 /etc/sysconfig/network-scripts/ifcfg-eth0.bak

3. Create alias files for secondary IPs

Secondary IP 1

sudo vi /etc/sysconfig/network-scripts/ifcfg-eth0:0

Add:

DEVICE=eth0:0
BOOTPROTO=none
ONBOOT=yes
IPADDR=192.168.1.101
PREFIX=24

Secondary IP 2

sudo vi /etc/sysconfig/network-scripts/ifcfg-eth0:1

Add:

DEVICE=eth0:1
BOOTPROTO=none
ONBOOT=yes
IPADDR=192.168.1.102
PREFIX=24

4. Apply and verify

sudo systemctl restart NetworkManager
ip addr show eth0

---

This article provides a step-by-step approach to assigning multiple secondary IPs across major Linux distributions.