How to add a second IP address, permanent or temporary in Linux

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If you want to add a secondary IP address to a NIC already in use in Linux, and have that change only temporary. Enter this command:

ifconfig [nic]:0 [IP-Address] netmask [mask] up

An example is shown below:

ifconfig eth0:0 192.168.1.2 netmask 255.255.255.0 up

You need to be root in order to execute that command.

If you prefer to use the ip command instead of ifconfig

ip address add [ip]/[mask-digits] dev [nic]

Here is an example:

ip address add 192.168.99.37/24 dev eth0

With this command you can add more ip address to the same dev NIC, the second is considered as secondary.

Ubuntu

For Ubuntu systems, edit the /etc/network/interfaces file

nano /etc/network/interfaces

Add this for one extra IP

auto [NIC]:[n]
iface [NIC]:[n] inet static
address [ip.add.rr.ss]
gateway [gw.ip.ad.rs]
netmask [ne.tm.as.kk]

Here an example:

auto eth0:1
iface eth0:1 inet static
address 192.168.0.1
gateway 192.168.0.254
netmask 255.255.255.0

You can add as many blocks as you want. Just change eth0:1 for eth0:2, eth0:3 and so on.

If you are adding additional IPs to eth1, or eth2 also modify that on the example.

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