Note: The multiple IP addresses must be in the same subnet to avoid multi-gateway issues. For example, if the subnet is 192.168.1.0/24 with gateway 192.168.1.1, you can assign IP addresses like 192.168.1.2 through 192.168.1.254.

To configure multiple IP addresses on a single network interface in CentOS, follow these steps:

1. Check Current Network Configuration

First, view the current network configuration to identify your interface name (e.g., eth0, ens33).

ip addr

2. Edit Network Configuration

CentOS 7 and later use nmcli (NetworkManager command-line tool) or direct editing of configuration files (e.g., /etc/sysconfig/network-scripts/ifcfg-<interface>). For newer versions, nmcli is recommended.

Using nmcli to Configure Multiple IPs

1. View existing connecsions:

   nmcli con show
   

2. Add an IP address to an existing connection:

   nmcli con mod <connection-name> +ipv4.addresses <IP-address>/<prefix>
   

   For example, to add IP 192.168.1.100/24 to connection ens33:

   nmcli con mod ens33 +ipv4.addresses 192.168.1.100/24
   

3. Apply the changes:

   nmcli con up <connection-name>
   

   Example:

   nmcli con up ens33
   

Editing Configuration Files (Traditional Method)

For CentOS 7 and earlier, or if you prefer direct editing:

1. Edit the interface configuration file, e.g., /etc/sysconfig/network-scripts/ifcfg-ens33.
2. Add multiple IP addresses using the following syntax:

   DEVICE=eth0
   BOOTPROTO=static
   ONBOOT=yes
   IPADDR0=192.168.1.101
   NETMASK0=255.255.255.0
   GATEWAY0=192.168.1.1
   IPADDR1=192.168.1.102
   NETMASK1=255.255.255.0
   GATEWAY1=192.168.1.1
   IPADDR2=192.168.1.103
   NETMASK2=255.255.255.0
   GATEWAY2=192.168.1.1
   

3. Save the file and restart the network service or reboot:

   systemctl restart network
   # or reboot: systemctl reboot
   

   Alternatively, restart the interface:

   ifdown eth0 && ifup eth0
   

3. Verify Configuration

Use ip addr or ifconfig to verify that the new IP addresses are active.

Notes:

• For CentOS 7 and later, prefer nmcli or NetworkManager over manual configuration files to avoid issues.
• For newer distributions like CentOS Stream or Fedora, refer to the latest documentation and use modern tools like nmcli.

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