CentOS Linux Networking

Add IP to CentOS 5/6

If you recently got a secondary IP block for your server but you do not know how to bind the secondary IP address, please follow the steps below:


First, run the following command to see which interface your server is using:



You will see an output like so:

eth0 Link encap:Ethernet HWaddr 00:0C:29:40:93:9C
inet addr: Bcast: Mask:
RX packets:1771 errors:0 dropped:0 overruns:0 frame:0
TX packets:359 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:138184 (134.9 KiB) TX bytes:49108 (47.9 KiB)
Interrupt:67 Base address:0x2000

lo   Link encap:Local Loopback
inet addr: Mask:
inet6 addr: ::1/128 Scope:Host
RX packets:390 errors:0 dropped:0 overruns:0 frame:0
TX packets:390 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:29204 (28.5 KiB) TX bytes:29204 (28.5 KiB)

In this scenario, you will be looking for the eth0 interface.  Now on to the actual command to bind the secondary ip!  Let’s say you get allocated an additional block of 3 ip addresses:,, with a netmask of, you would do the following:


ifconfig eth0:1 netmask
ifconfig eth0:1 up
ifconfig eth0:2 netmask
ifconfig eth0:2 up
ifconfig eth0:3 netmask
ifconfig eth0:3 up 

If you want the new IP’s to be brought up automatically upon reboots, you can add these commands to the file: /etc/rc.local

That’s all there is to it!

Related Articles

  • Disable SELinux

    Security-Enhanced Linux (SELinux) is a mandatory access control (MAC) security mechanism implemented in the Linux kernel. This mechanism adds an extra layer of access security to your files,directories,devices, ports and...
  • Some useful ‘find’ commands

    The ‘find’ command is quite useful as it helps to identify files with specific permissions, users,groups, size, etc.  Also, it is quite helpful to as it allows to process its results...
  • Using MTR

    MTR is a powerful network diagnostic tool that enables administrators to diagnose and isolate networking errors and provide helpful reports of network status to upstream providers. MTR represents an evolution...
  • Top Open Source applications.

    These are a collection of some useful Open Source office application that are helpful by increasing productivity. Often a person would be limited in buying an expensive piece of software...