Login as root
then enter command
nano /etc/network/interfaces
If have something like this on that file
iface enp1s0f0 inet static
address 123.124.125.40
netmask 255.255.255.0
gateway 123.444.123.1
Then to add additional ips, have it like this
iface enp1s0f0 inet static
address 123.124.125.40
netmask 255.255.255.0
gateway 123.444.123.1
iface enp1s0f0 inet static
address 123.124.125.41
netmask 255.255.240.0
iface enp1s0f0 inet static
address 123.124.125.42
netmask 255.255.240.0
iface enp1s0f0 inet static
address 123.124.125.43
netmask 255.255.255.0
In the above, first 1 is main ip and rest of them are additional ips. enp1s0f0
might vary system to system. After that restart network using safe way:
ifdown enp1s0f0 && ifup enp1s0f0
Check the ips using:
ip addr
The restart
Source: https://www.reddit.com/r/linuxquestions/comments/cfl0mj/how_do_i_add_an_additional_ip_address_to/
Also read: https://askubuntu.com/a/547300