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How to Create Multiple IP Addresses on One Network Interface

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How to Create Multiple IP Addresses on One Network Interface


The concept of creating or configuring multiple IP addresses on a single network interface is called IP aliasing, which is very useful for setting up multiple virtual sites on a web server using one single network interface with different IP addresses on a single subnet network.

The main advantage of using this IP aliasing is that you don’t need to have a physical adapter attached to each IP. Instead, you can create multiple or many virtual interfaces (aliases) for a single physical card.

The instructions given here apply to all RHEL-based distributions such as Fedora, CentOS, Rocky, and Alma Linux. Creating multiple interfaces and assigning IP addresses to them manually is a daunting task.

Here, we’ll see how to assign IP addresses by defining a set of IP ranges. We’ll also understand how to create a virtual interface and assign a different range of IP addresses to it all at once.

In this article, we used LAN IPs, so replace those with the ones you will be using.

How to Create Multiple IP Addresses to Single Network Interface

Here, I have an interface named ‘ifcfg-eth0‘, which is the default network interface card for the ethernet device. If you’ve connected a second ethernet device, it will appear as ‘ifcfg-eth1‘, and so on for each additional device.

These network files for the devices are found in the ‘/etc/sysconfig/network-scripts/‘ directory and you can list all devices using the following ls command.

ls -l /etc/sysconfig/network-scripts/

Sample Output:

ifcfg-eth0   ifdown-isdn    ifup-aliases  ifup-plusb     init.ipv6-global
ifcfg-lo     ifdown-post    ifup-bnep     ifup-post      net.hotplug
ifdown       ifdown-ppp     ifup-eth      ifup-ppp       network-functions
ifdown-bnep  ifdown-routes  ifup-ippp     ifup-routes    network-functions-ipv6
ifdown-eth   ifdown-sit     ifup-ipv6     ifup-sit
ifdown-ippp  ifdown-tunnel  ifup-isdn     ifup-tunnel
ifdown-ipv6  ifup           ifup-plip     ifup-wireless

Let’s assume that we want to create three additional virtual interfaces to bind three IP addresses (172.16.16.126, 172.16.16.127, and 172.16.16.128) to the NIC.

So, we need to create three additional alias files, while “ifcfg-eth0” keeps the same primary IP address. This is how we move forward to set up three aliases to bind the following IP addresses.

Adapter            IP Address                Type
-------------------------------------------------
eth0              172.16.16.125            Primary
eth0:0            172.16.16.126            Alias 1
eth0:1            172.16.16.127            Alias 2
eth0:2            172.16.16.128            Alias 3

Where ":X" represents the device (interface) number for creating aliases for interface eth0. For each alias, you must assign a number sequentially.

For example, we copy existing parameters from the interface “ifcfg-eth0” to virtual interfaces named ifcfg-eth0:0, ifcfg-eth0:1, and ifcfg-eth0:2.

Navigate to the network directory and create the files as shown below.

cd /etc/sysconfig/network-scripts/
cp ifcfg-eth0 ifcfg-eth0:0
cp ifcfg-eth0 ifcfg-eth0:1
cp ifcfg-eth0 ifcfg-eth0:2

Open a file “ifcfg-eth0” and view the contents.

vi ifcfg-eth0

Sample Output:

DEVICE="eth0"
BOOTPROTO=static
ONBOOT=yes
TYPE="Ethernet"
IPADDR=172.16.16.125
NETMASK=255.255.255.224
GATEWAY=172.16.16.100
HWADDR=00:0C:29:28:FD:4C

Here, we only need two parameters (DEVICE and IPADDR). So, open each file with your favorite editor, rename the DEVICE name to its corresponding alias, and change the IPADDR address.

For example, open files ‘ifcfg-eth0:0‘, ‘ifcfg-eth0:1‘, and ‘ifcfg-eth0:2‘ using the VI editor and update both parameters.

Finally, it will look similar to the example below.

ifcfg-eth0:0
DEVICE="eth0:0"
BOOTPROTO=static
ONBOOT=yes
TYPE="Ethernet"
IPADDR=172.16.16.126
NETMASK=255.255.255.224
GATEWAY=172.16.16.100
HWADDR=00:0C:29:28:FD:4C
ifcfg-eth0:1
DEVICE="eth0:1"
BOOTPROTO=static
ONBOOT=yes
TYPE="Ethernet"
IPADDR=172.16.16.127
NETMASK=255.255.255.224
GATEWAY=172.16.16.100
HWADDR=00:0C:29:28:FD:4C
ifcfg-eth0:2
DEVICE="eth0:2"
BOOTPROTO=static
ONBOOT=yes
TYPE="Ethernet"
IPADDR=172.16.16.128
NETMASK=255.255.255.224
GATEWAY=172.16.16.100
HWADDR=00:0C:29:28:FD:4C

Once, you’ve made all changes, save all your changes and restart/start the network service for the changes to reflect.

systemctl restart network

To verify all the aliases (virtual interface) are up and running, you can use “ifconfig” or “ip” command.

ifconfig

Sample Output:

eth0      Link encap:Ethernet  HWaddr 00:0C:29:28:FD:4C
          inet addr:172.16.16.125  Bcast:172.16.16.100  Mask:255.255.255.224
          inet6 addr: fe80::20c:29ff:fe28:fd4c/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:237 errors:0 dropped:0 overruns:0 frame:0
          TX packets:198 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:25429 (24.8 KiB)  TX bytes:26910 (26.2 KiB)
          Interrupt:18 Base address:0x2000

eth0:0    Link encap:Ethernet  HWaddr 00:0C:29:28:FD:4C
          inet addr:172.16.16.126  Bcast:172.16.16.100  Mask:255.255.255.224
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:18 Base address:0x2000

eth0:1    Link encap:Ethernet  HWaddr 00:0C:29:28:FD:4C
          inet addr:172.16.16.127  Bcast:172.16.16.100  Mask:255.255.255.224
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:18 Base address:0x2000

eth0:2    Link encap:Ethernet  HWaddr 00:0C:29:28:FD:4C
          inet addr:172.16.16.128  Bcast:172.16.16.100  Mask:255.255.255.224
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:18 Base address:0x2000

Now try to ping each of them from a different machine. If everything is set up correctly, you will receive a ping response from each of them.

ping 172.16.16.126
ping 172.16.16.127
ping 172.16.16.128

Sample Output:

ping 172.16.16.126
PING 172.16.16.126 (172.16.16.126) 56(84) bytes of data.
64 bytes from 172.16.16.126: icmp_seq=1 ttl=64 time=1.33 ms
64 bytes from 172.16.16.126: icmp_seq=2 ttl=64 time=0.165 ms
64 bytes from 172.16.16.126: icmp_seq=3 ttl=64 time=0.159 ms

ping 172.16.16.127
PING 172.16.16.127 (172.16.16.127) 56(84) bytes of data.
64 bytes from 172.16.16.127: icmp_seq=1 ttl=64 time=1.33 ms
64 bytes from 172.16.16.127: icmp_seq=2 ttl=64 time=0.165 ms
64 bytes from 172.16.16.127: icmp_seq=3 ttl=64 time=0.159 ms

ping 172.16.16.128
PING 172.16.16.128 (172.16.16.128) 56(84) bytes of data.
64 bytes from 172.16.16.128: icmp_seq=1 ttl=64 time=1.33 ms
64 bytes from 172.16.16.128: icmp_seq=2 ttl=64 time=0.165 ms
64 bytes from 172.16.16.128: icmp_seq=3 ttl=64 time=0.159 ms

It appears that everything is working smoothly. With these new IPs, you can set up virtual sites in Apache, FTP accounts, and many other things.

Assign Multiple IP Addresses Range

If you would like to create a range of multiple IP addresses to a particular interface called “ifcfg-eth0“, we use “ifcfg-eth0-range0” and copy the contents of ifcfg-eth0 on it as shown below.

cd /etc/sysconfig/network-scripts/
cp -p ifcfg-eth0 ifcfg-eth0-range0

Now open the “ifcfg-eth0-range0” file.

vi ifcfg-eth0-range0

and add “IPADDR_START” and “IPADDR_END” IP address ranges as shown below.

#DEVICE="eth0"
#BOOTPROTO=none
#NM_CONTROLLED="yes"
#ONBOOT=yes
TYPE="Ethernet"
IPADDR_START=172.16.16.126
IPADDR_END=172.16.16.130
IPV6INIT=no
#GATEWAY=172.16.16.100

Save it and restart/start the network service

systemctl restart network

Verify that virtual interfaces are created with IP Addresses.

ifconfig

Sample Output:

eth0      Link encap:Ethernet  HWaddr 00:0C:29:28:FD:4C
          inet addr:172.16.16.125  Bcast:172.16.16.100  Mask:255.255.255.224
          inet6 addr: fe80::20c:29ff:fe28:fd4c/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1385 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1249 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:127317 (124.3 KiB)  TX bytes:200787 (196.0 KiB)
          Interrupt:18 Base address:0x2000

eth0:0     Link encap:Ethernet  HWaddr 00:0C:29:28:FD:4C
          inet addr:172.16.16.126  Bcast:172.16.16.100  Mask:255.255.255.224
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:18 Base address:0x2000

eth0:1    Link encap:Ethernet  HWaddr 00:0C:29:28:FD:4C
          inet addr:172.16.16.127  Bcast:172.16.16.100  Mask:255.255.255.224
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:18 Base address:0x2000

eth0:2    Link encap:Ethernet  HWaddr 00:0C:29:28:FD:4C
          inet addr:172.16.16.128  Bcast:172.16.16.100  Mask:255.255.255.224
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:18 Base address:0x2000

eth0:3    Link encap:Ethernet  HWaddr 00:0C:29:28:FD:4C
          inet addr:172.16.16.129  Bcast:172.16.16.100  Mask:255.255.255.224
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:18 Base address:0x2000

eth0:4    Link encap:Ethernet  HWaddr 00:0C:29:28:FD:4C
          inet addr:172.16.16.130  Bcast:172.16.16.100  Mask:255.255.255.224
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:18 Base address:0x2000

By following these methods, you can effectively create and manage multiple IP addresses on a single network interface in Red Hat Enterprise Linux systems. This flexibility enables you to optimize network communication and connectivity according to your specific requirements.



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