How to assign multiple IP addresses to one network interface on CentOS

Last updated on October 11, 2020 by Dan Nanni

The practice of configuring multiple IP addresses on a particular network interface is called IP aliasing. IP aliasing is useful when you set up multiple sites on virtual web hosting on a single interface, or maintain multiple connections to a network each of which serves a different purpose. You can assign multiple IP addresses to one network interface from a single subnet or completely different ones.

All existing Linux distributions including CentOS supports IP aliasing. Here is how to bind multiple IP addresses to a single network interface on CentOS.

If you would like to set up IP aliasing on the fly, there are two ways to do it. One way is to use ifconfig, and the other method is to use ip command. Using these two methods, let me show you how to add two extra IP addresses to eth0.

Set up IP Aliasing with ifconfig

To use the first method:

$ sudo ifconfig eth0:1 192.168.10.10 netmask 255.255.255.0 up
$ sudo ifconfig eth0:2 192.168.10.15 netmask 255.255.255.0 up

Set up IP Aliasing with ip

To use the second method:

$ sudo ip addr add 192.168.10.10/24 dev eth0
$ sudo ip addr add 192.168.10.15/24 dev eth0

View IP Aliases Defined by ifconfig or ip

To view a list of all IP addresses assigned to eth0 by using either method, run the following command.

$ sudo ip addr list dev eth0

2: eth0:  mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 1000
    link/ether 00:0c:29:5c:86:f4 brd ff:ff:ff:ff:ff:ff
    inet 192.168.91.128/24 brd 192.168.91.255 scope global eth0
    inet 192.168.91.10/24 scope global secondary eth0
    inet 192.168.91.20/24 scope global secondary eth0
    inet6 fe80::20c:29ff:fe5c:86f4/64 scope link
       valid_lft forever preferred_lft forever

If you used ifconfig to create IP aliases, you can also use the same command to view them.

$ ifconfig -a

eth0      Link encap:Ethernet  HWaddr 00:0C:29:5C:86:F4
          inet addr:192.168.91.128  Bcast:192.168.91.255  Mask:255.255.255.0
          inet6 addr: fe80::20c:29ff:fe5c:86f4/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:22 errors:0 dropped:0 overruns:0 frame:0
          TX packets:102 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:3869 (3.7 KiB)  TX bytes:18172 (17.7 KiB)
          Interrupt:19 Base address:0x2000

eth0:1    Link encap:Ethernet  HWaddr 00:0C:29:5C:86:F4
          inet addr:192.168.91.10  Bcast:192.168.91.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:19 Base address:0x2000

eth0:2    Link encap:Ethernet  HWaddr 00:0C:29:5C:86:F4
          inet addr:192.168.91.20  Bcast:192.168.91.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:19 Base address:0x2000

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:8 errors:0 dropped:0 overruns:0 frame:0
          TX packets:8 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:480 (480.0 b)  TX bytes:480 (480.0 b)

If you would like to permanently assign multiple IP addresses to an interface, create corresponding configuration files in /etc/sysconfig/network-scripts.

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

DEVICE=eth0:1
BOOTPROTO=static
IPADDR=192.168.0.5
NETMASK=255.255.255.0
ONBOOT=yes

Once you have created as many configuration files as IP addresses to assign, restart network to activate IP aliasing.

$ sudo /etc/init.d/network restart

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