How to Add Virtual IP adddress on GNU / Linux -
Set up multiple IP addresses on Linux boot with ifconfig
Periodically, I have to set-up new Linux servers with second, third
in other words multiple IP addresses.
Anyone who needs to set up multiple IP addresses to be responding
on one machine knows the common reason is a need is multiple domain
names with SSL enabled hosted on the same physical server.
Configuring different domain names to be resolved to different IPs
is rare but for some case scenarios is a must. Some other use case
is if running other popular Network services like,
Apache
VirtualHost,
Qmail + (vpopmail POP3, FTP servers, proxies
etc.
The universal way which allows to
set multiple virtual IP
addresses on GNU / Linux gives the admin an option as both
ifconfig or ip commands can be used.
I personally always use ifconfig so I always use ifconfig to set
new virtual IP addreses and interfaces.
1. Adding virtual ethernet interface and Virtual IP on Slackware
and across all Linuxes with ifconfig
Adding a virtual ethernet interfaces with ifconfig command
is done using the syntax:
/sbin/ifconifg eth0:0 IP_ADDR0 netmask NETMASK_IP_ADDR
up
/sbin/ifconfig eth0:1 IP_ADDR1 netmask NETMASK_IP_ADDR1 up
/sbin/ifconfig eth0:N IP_ADDR1 netmask NETMASK_IPADDRN up
...
Hence to add the 4 IP addresses:
1.2.3.41.2.3.51.2.3.71.2.5.8
use something like:
server:~# /sbin/ifconfig eth0:0 1.2.3.4 netmask 255.255.255.0
up
server:~# /sbin/ifconfig eth0:1 1.2.3.5 netmask 255.255.255.0
up
server:~# /sbin/ifconfig eth0:2 1.2.3.7 netmask 255.255.255.0
up
server:~# /sbin/ifconfig eth0:3 1.2.5.8 netmask 255.255.255.0
up
...
server:~# /sbin/ifconfig ethX:N x.x.x.x netmask 255.255.255.0
up
2. Setting Virtual IP addresses on interfaces on
system boot time
To set a number of IP addresses to automatically be bringed up on
server boot, simply place in
/etc/rc.local before the
exit 0 - last file line;
export IP_ADDRESS1='1.2.3.4';
export IP_ADDRESS2='1.2.3.5';
export IP_ADDRESS3='1.2.3.8';
export IP_ADDRESS4='1.2.3.9';
/sbin/ifconfig eth0:0 $IP_ADDRESS1 netmask 255.255.255.0 up
/sbin/ifconfig eth0:1 $IP_ADDRESS2 netmask 255.255.255.0 up
/sbin/ifconfig eth0:2 $IP_ADDRESS3 netmask 255.255.255.0 up
/sbin/ifconfig eth0:3 $IP_ADDRESS3 netmask 255.255.255.0
up
3. Adding new virtual IP addresses to server to /etc/rc.local
from command line
To do add a set of virtual IP addresses to
/etc/rc.local
without using an interactive text editor (useful for scripting
purposes) use:
server:~# head -n $(($(echo $(wc -l /etc/rc.local |awk
'{ print $1 }')) - 1)) /etc/rc.local >>
/etc/rc.local.tmp
server:~# echo "export IP_ADDRESS1='1.2.3.4'" >>
/etc/rc.local.tmp;
server:~# echo "export IP_ADDRESS2='1.2.3.5'" >>
/etc/rc.local.tmp
server:~# echo "export IP_ADDRESS3='1.2.3.8'" >>
/etc/rc.local.tmp
server:~# echo "export IP_ADDRESS4='1.2.3.9'" >>
/etc/rc.local.tmp
server:~# echo "/sbin/ifconfig eth0:0 $IP_ADDRESS1 netmask
255.255.255.0 up" >>/etc/rc.local.tmp
server:~# echo "/sbin/ifconfig eth0:1 $IP_ADDRESS2 netmask
255.255.255.0 up" >> /etc/rc.local.tmp
server:~# echo "/sbin/ifconfig eth0:2 $IP_ADDRESS3 netmask
255.255.255.0 up" >> /etc/rc.local.tmp
server:~# echo "/sbin/ifconfig eth0:3 $IP_ADDRESS3 netmask
255.255.255.0 up" >> /etc/rc.local.tmp
server:~# echo "exit 0" >> /etc/rc.local.tmp
server:~# cp -rpf /etc/local /etc/local.bak; cp -rpf
/etc/rc.local.tmp /etc/rc.local
4. Setting up Virtual IP addresses on Debian and Ubuntu
G*/Linux
In Debian and other (deb) based Linux distributions (Ubuntu, Mint
etc.), there is also another approach to "solve" the task through
using the default networking config file:
/etc/network/interfaces
Hence if managing any deb one based Linux, its a good practice in
terms of clarity to use the
"debian way" to add virutal ip
addresses.
On these distros to add new virtual ip address edit
/etc/network/interfaces with your favourite text editor, for
instance:
# vim /etc/network/interfaces
Place inside config like:
auto eth0:1
iface eth0:1 inet static
address 192.168.1.60
netmask 255.255.255.0
network x.x.x.x
broadcast x.x.x.x
gateway x.x.x.x
N.B. Be cautious or you will end up with your server being
unreachable, make sure you put some crontab to periodically check
and up the main eth0 assigned IP address to prevent server
inaccessibility if you don't have a physical server access.
For more Virtual IPs just add more entries like the above ones
...
5. Setting up Virtual IP addresses on Redhat based distros
(RHEL, CentOS, Fedora)
In Fedora, CentOS, RHEL each new virtual IP or virtual IP range has
to go in a separate file like:
- /etc/sysconfig/network-scripts/ifcfg-eth0:0
- /etc/sysconfig/network-scripts/ifcfg-eth0:1
- /etc/sysconfig/network-scripts/ifcfg-eth0:2
- ...
Each of the
ifcfg-eth0:N files could be a straight copy of
/etc/sysconfig/network-scripts/ifcfg-eth0
[root@centos:~]# cp /etc/sysconfig/network-scripts/ifcfg-eth0
/etc/sysconfig/network-scripts/ifcfg-eth0:0
[root@centos:~]# vim
/etc/sysconfig/network-scripts/ifcfg-eth0:0
The default content of
ifcfg-eth0:0 should be like:
NETMASK=255.255.255.0
DEVICE=eth0
ONBOOT=yes
TYPE=Ethernet
ETHTOOL_OPTS="duplex full speed 100 autoneg off wol g"
IPADDR=10.0.0.01
You will have to change the fields you see in red to be like:
DEVICE=eth0:0
IPADDR=10.0.0.02
Further on for all virtual IPs create files
/etc/sysconfig/network-scripts/ifcfg-ethN and change
DEVICE and IPADDR value.
Finally to load up the new Virtual IP interfaces to come online
restart networking:
/sbin/service network restart
...
Check and re-check that the IP configs placed are correct,
otherwise if you do it on a remote server you will loose connection
to it as it could happen the primary server IP on eth0 fails
to properly set.