Configuring IP aliasing

Last updated 27th November, 2017

Objective

IP aliasing is a special network configuration of your dedicated server, which allows you to associate multiple IP addresses with a single network interface.

This guide explains how to make this addition.

Requirements

• You must have a dedicated server (VPS, dedicated server or Public Cloud instance).
• You must have one or more failover IPs.
• You must be connected via SSH to the server (root access).

Instructions

Here are the configurations for the main distributions/operating systems.

Debian 6/7/8 and derivatives

Step 1: Create the source file

First, make a copy of the source file, so that you can revert at any time:

cp /etc/network/interfaces /etc/network/interfaces.bak

Step 2: Edit the source file

You can now modify the source file:

editor /etc/network/interfaces

You then need to add a secondary interface:

auto eth0:0
iface eth0:0 inet static
address IP_FAIL_OVER
netmask 255.255.255.255

To ensure that the secondary interface is enabled when the eth0 interface is also enabled, you need to add the following line to the eth0 configuration:

post-up /sbin/ifconfig eth0:0 IP_FAIL_OVER netmask 255.255.255.255 broadcast IP_FAIL_OVER
pre-down /sbin/ifconfig eth0:0 down

If you have two failover IPs to configure, the /etc/network/interfaces file should look like this:

auto eth0
iface eth0 inet static
address SERVER_IP
netmask 255.255.255.0
broadcast xxx.xxx.xxx.255
gateway xxx.xxx.xxx.254

auto eth0:0
iface eth0:0 inet static
address IP_FAIL_OVER1
netmask 255.255.255.255

auto eth0:1
iface eth0:1 inet static
address IP_FAIL_OVER2
netmask 255.255.255.255

# IPFO 1
post-up /sbin/ifconfig eth0:0 IP_FAIL_OVER1 netmask 255.255.255.255 broadcast IP_FAIL_OVER1
pre-down /sbin/ifconfig eth0:0 down

# IPFO 2
post-up /sbin/ifconfig eth0:1 IP_FAIL_OVER2 netmask 255.255.255.255 broadcast IP_FAIL_OVER2
pre-down /sbin/ifconfig eth0:1 down

Step 3: Restart the interface

You now need to restart your interface:

/etc/init.d/networking restart

Debian 9+, Ubuntu 17+, Fedora 26+ and Arch Linux

On these distributions, the naming of interfaces as eth0, eth1 (and so on) is abolished, and we will now use the systemd-network more generally.

Step 1: Create the source file

First, make a copy of the source file, so that you can revert at any time:

cp /etc/systemd/network/50-default.network /etc/systemd/network/50-default.network.bak

Step 2: Edit the source file

You can now add your failover IP to the source file, as follows:

nano /etc/network/50-default.network

[Address]
Address=22.33.44.55/32
Label=failover1 # optional

The label is optional. It’s just for distinguishing between your various failover IPs.

Step 3: Restart the interface

You now need to restart your interface:

systemctl restart systemd-network

CentOS and Fedora (25 and earlier)

Step 1: Create the source file

First, make a copy of the source file so that you can use it as a template:

cp /etc/sysconfig/network-scripts/ifcfg-eth0 /etc/sysconfig/network-scripts/ifcfg-eth0:0

Step 2: Edit the source file

You can now modify the eth0:0 file in order to replace the IP:

editor /etc/sysconfig/network-scripts/ifcfg-eth0:0

First, replace the name of the device, then replace the existing IP with the failover IP you have received:

DEVICE="eth0:0"
ONBOOT="yes"
BOOTPROTO="none" # For CentOS use "static"
IPADDR="IP_FAIL_OVER"
NETMASK="255.255.255.255"
BROADCAST="IP_FAIL_OVER"

Step 3: Restart the interface

You now need to restart your interface:

ifup eth0:0

Gentoo

Step 1: Create the source file

First, make a copy of the source file, so that you can revert at any time:

cp /etc/conf.d/net /etc/conf.d/net.bak

Step 2: Edit the source file

Now you have to edit the file to add the failover IP. In Gentoo, an alias is added directly in the eth0 interface. We do not create an eth0:0 interface like in Red Hat or CentOS.

All you need to do is add a line break after the netmask 255.255.255.0 and add your failover IP (SERVER_IP must be replaced by your server’s primary IP).

editor /etc/conf.d/net

Therefore, you need to add the following:

config_eth0=( "SERVER_IP netmask 255.255.255.0" "IP_FAIL_OVER netmask 255.255.255.255 brd IP_FAIL_OVER" )

The /etc/conf.d/net file must contain the following:

#This blank configuration will automatically use DHCP for any net.
# scripts in /etc/init.d. To create a more complete configuration,
# please review /etc/conf.d/net.example and save your configuration
# in /etc/conf.d/net (this file :]!).
config_eth0=( "SERVER_IP netmask 255.255.255.0"
"IP_FAIL_OVER netmask 255.255.255.255 brd IP_FAIL_OVER" )
routes_eth0=( "default gw SERVER_IP.254" )

In order to ping your failover IP, simply restart the network interface.

Step 3: Restart the interface

You now need to restart your interface:

/etc/init.d/net.eth0 restart

openSUSE

Step 1: Create the source file

First, make a copy of the source file, so that you can revert at any time:

cp /etc/sysconfig/network/ifcfg-ens32 /etc/sysconfig/network/ifcfg-ens32.bak

Step 2: Edit the source file

You then need to edit the /etc/sysconfig/network/ifcfg-ens32 file as follows:

IPADDR_1=FIP_FAIL_OVER
NETMASK_1=255.255.255.255
LABEL_1=ens32:0

cPanel

Step 1: Create the source file

First, make a copy of the source file, so that you can revert at any time:

cp /etc/ips /etc/ips.bak

Step 2: Edit the source file

You then need to edit the /etc/ips file:

editor /etc/ips

Then add the failover IP to the file:

IP_FAIL_OVER:255.255.255.255:IP_FAIL_OVER

Next, add the IP in: ``

/etc/ipaddrpool`:

IP_FAIL_OVER

Step 3: Restart the service

You now need to restart your interface:

/etc/init.d/ipaliases restart

Windows Server

Windows servers are often DHCP-enabled in the network configuration. If you have already set up a failover IP or switched your configuration to a fixed IP, go directly to the next step.

Otherwise, you need to first switch from a network-level DHCP configuration to a fixed IP configuration.

Open the command prompt cmd or powershell, then type the following command:

ipconfig /all

This will return the following, for example:

Identify and write down your IPv4, subnet mask, default gateway and the name of the network interface controller (network adapter).

In our example, the server IP is: 94.23.229.151

You can perform the next steps via either a command-line interface or the graphical user interface:

Via a command-line interface (recommended)

In the commands below, you need to replace:

In the command prompt:

1. Switch to a fixed IP

netsh interface ipv4 set address name="NETWORK_ADAPTER" static IP_ADDRESS SUBNET_MASK GATEWAY

1. Set the DNS server

netsh interface ipv4 set dns name="NETWORK_ADAPTER" static 213.186.33.99

1. Add a failover IP

netsh interface ipv4 add address "NETWORK_ADAPTER" IP_ADDRESS_FAILOVER 255.255.255.255

Your failover IP is now functional.

Via the graphical user interface

1. Go to Start> Control Panel>Network and Internet> Network and Sharing Centre> Change Adapter Settings(in the left-hand menu).
2. Right-click on Local Area Connection.
3. Click on Properties.
4. Select Internet Protocol Version 4 (TCP/IPv4), then click on Properties.
5. Click on "Use the following IP address" and type in your server’s primary IP, subnet mask and default gateway information obtained by using the ipconfig command above. (In the "Preferred DNS Server" box, type 213.186.33.99.)

Then click on Advanced (still in the TCP/IP Settings.

In the IP Address section, click Add:

Type in your failover IP and the subnet mask 255.255.255.255.

Click on Add.

Your failover IP is now functional.

FreeBSD

Step 1: Determine the interface

Determine the name of your primary network interface. You can use the ifconfig command for this operation:

ifconfig

This will return the following:

ifconfig
>>> nfe0: flags=8843 metric 0 mtu 1500
>>> options=10b
>>> ether 00:24:8c:d7:ba:11
>>> inet 94.23.196.18 netmask 0xffffff00 broadcast 94.23.196.255
>>> inet 87.98.129.74 netmask 0xffffffff broadcast 87.98.129.74
>>> media: Ethernet autoselect (100baseTX )
>>> status: active
>>> lo0: flags=8049 metric 0 mtu 16384
>>> options=3
>>> inet6 fe80::1%lo0 prefixlen 64 scopeid 0x2
>>> inet6 ::1 prefixlen 128
>>> inet 127.0.0.1 netmask 0xff000000 v comsdvt#

In our example, the name of the interface is therefore nfe0.

Step 2: Create the source file

First, make a copy of the source file, so that you can revert at any time:

cp /etc/rc.conf /etc/rc.conf.bak

Step 3: Edit the source file

Edit the /etc/rc.conf file:

editor /etc/rc.conf

Then add this line at the end of the file: ifconfig _INTERFACE_alias0=inet IP_FAIL_OVER netmask 255.255.255.255 broadcast IP_FAIL_OVER.

Replace INTERFACE and IP_FAIL_OVER respectively with the name of your interface (identified in the first step) and your failover IP. Here is an example:

ifconfig_nfe0_alias0="inet 87.98.129.74 netmask 255.255.255.255 broadcast 87.98.129.74"

Step 4: Restart the interface

You now need to restart your interface:

/etc/rc.d/netif restart && /etc/rc.d/routing restart

Solaris

Step 1: Determine the interface

Determine the name of your primary network interface. You can use the ifconfig command for this operation:

ifconfig -a

This will return the following:

ifconfig -a
>>> lo0: flags=2001000849 mtu 8232 index 1 inet 127.0.0.1 netmask ff000000 e1000g0: flags=1000843 mtu 1500 index 2 inet 94.23.41.167 netmask ffffff00 broadcast 94.23.41.255 ether 0:1c:c0:f2:be:42

In our example, the name of the interface is therefore e1000g0.

Step 2: Create the source file

First, make a copy of the source file, so that you can revert at any time:

editor /etc/hostname.e1000g0:1

Step 3: Edit the source file

In this file, enter the following: IP_FAIL_OVER/32 up, where IP_FAIL_OVER is your failover IP. For example:

188.165.171.40/32 up

Step 4: Restart the interface

You now need to restart your interface:

svcadm restart svc:/network/physical:default

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