Multiple IP address on Single NIC (Redhat/Fedora)

We can setup two Ipaddress on single NIC.

Below i have mentioned for Redhat/Fedora/CentOs system.

STEP 1 : (Initial/First IP address)

#cat /etc/sysconfig/network-scripts/ifcfg-eth0

DEVICE=eth0
BOOTPROTO=static
BROADCAST=10.8.0.255
IPADDR=10.8.0.10
NETMASK=255.255.255.0
NETWORK=10.8.0.0
ONBOOT=yes

STEP 2 : (Second IP address)
#cat /etc/sysconfig/network-scripts/ifcfg-eth0:1

DEVICE=eth0:1
BOOTPROTO=static
BROADCAST=10.8.0.255
IPADDR=10.8.0.11
NETMASK=255.255.255.0
NETWORK=10.8.0.0
ONBOOT=yes

View Routing Table and Change your default Gateway

The netstat -nr command will provide the contents of the touting table.

# netstat -nr

Kernel IP routing table

Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface

10.8.0.0        0.0.0.0         255.255.255.0   U         0 0          0 eth0

169.254.0.0     0.0.0.0         255.255.0.0     U         0 0          0 eth0

0.0.0.0         10.8.0.1        0.0.0.0         UG        0 0          0 eth0

Change Your Default Gateway

You will need to update your /etc/sysconfig/network file to reflect the change. This file is used to configure your default gateway

NETWORKING=yes
HOSTNAME=newhost
GATEWAY=10.8.0.2

Network configuration for Debian

Ip from dhcp

#/etc/network/interfaces
# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet dhcp

For a static IP

#/etc/network/interfaces
# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet static
address 10.8.0.100
netmask 255.255.255.0
gateway 10.8.0.1
broadcast 10.8.0.255

How to add multiple IP addresses manually

# ifconfig

will output all the configured addresses

eth0: inet addr:10.8.0.10 Bcast:10.8.0.255 Mask:255.255.255.0

To add on extra IP addresses execute below command:

# ifconfig eth0:1 10.8.0.12 netmask 255.255.255.0

For additional IP addresses, make sure you increment the 1 in eth0:1

Third ip address would be like this

# ifconfig eth0:2 10.8.0.13 netmask 255.255.255.0

Assigning a virtual IP to a NIC

Assigning a virtual IP to a NIC is a very easy task either you use the system-config-network tool or just do some text file editing. The script ifconfig can also be used to create a virtual network interface, but this would not be permanent since the changes ifconfig makes do not survive a reboot.

In Fedora, all information about the network interfaces is kept in the following directories:

• /etc/sysconfig/network-scripts/
• /etc/sysconfig/networking/

My NIC configuration script is /etc/sysconfig/network-scripts/ifcfg-eth0 looks like this:

DEVICE=eth0

BOOTPROTO=static

BROADCAST=192.168.0.255

HWADDR=00:00:00:00:00:00

IPADDR=192.168.0.1

NETMASK=255.255.255.0

NETWORK=192.168.0.0

ONBOOT=yes

TYPE=Ethernet

GATEWAY=192.168.0.254

Make a copy of this in the same directory naming the new file ifcfg-eth0:1

# cp ifcfg-eth0 ifcfg-eth0\:1

Modification in file ifcfg-eth0\:1 is shown in bold

DEVICE=eth0:1

BOOTPROTO=static

BROADCAST=192.168.0.255

HWADDR=00:00:00:00:00:00

IPADDR=192.168.0.101

NETMASK=255.255.255.0

NETWORK=192.168.0.0

ONBOOT=yes

TYPE=Ethernet

GATEWAY=192.168.0.254

So, its IP address will be 192.168.0.101. Save the file and copy it to/etc/sysconfig/networking/devices/:

# cp ifcfg-eth0\:1 /etc/sysconfig/networking/devices/

Also, copy it to your default network profile or whichever profile you use:

# cp ifcfg-eth0\:1 /etc/sysconfig/networking/profiles/default/

Now, bring up the new interface using the ifup script:

# ifup eth0\:1

Running ifconfig, the new interface should be listed. You can also check it by pinging:

# ping 192.168.0.101