Adding Alias IP to a NIC

http://www.cyberciti.biz/faq/linux-creating-or-adding-new-network-alias-to-a-network-card-nic/

Using ifconfig command line
You can use ifconfig command to configure a network interface and alias. For example:

    * eth0 NIC IP – 192.168.1.5
    * eth0:0 first NIC alias: 192.168.1.6

To setup eth0:0 alias type the following command as the root user:

# ifconfig eth0:0 192.168.1.6 up

Verify alias is up and running using following command:

# ifconfig –a
# ping 192.168.1.6

However if you reboot system you will lost your alias. To make it permanent you need to add it network configuration file:

If you are using Debian Linux
Open the file /etc/network/interfaces:

# vi /etc/network/interfaces

Append text as follows:

auto eth0:1
iface eth0:1 inet static
name Ethernet alias LAN card
address 192.168.1.7
netmask 255.255.255.0
broadcast 192.168.1.255
network 192.168.1.0

Save the file and restart the network:

# /etc/init.d/networking restart

If you are using Red Hat / Fedora Linux
Copy etc/sysconfig/network-scripts/ifcfg-eth0 file etc/sysconfig/network-scripts/ifcfg-eth0:0 -

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

Open file /etc/sysconfig/network-scripts/ifcfg-eth0:0 using vi text editor:

# vi /etc/sysconfig/network-scripts/ifcfg-eth0:0

Find entry that read as follows:

DEVICE=eth0

Replace with:

DEVICE=eth0:0

Find entry that read as follows:

IPADDR=xxx.xxx.xxx.xxx

Replace it with your actual IP address:

IPADDR=192.168.1.7

At the end your file should like as follows:

DEVICE=eth0:0
IPADDR=192.168.1.7
NETMASK=255.255.255.0
NETWORK=192.168.1.0
ONBOOT=yes
NAME=eth0:0

Open file /etc/sysconfig/network-scripts/ifcfg-eth0 and make sure file does not have a GATEWAY= entry:

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

Find the entry that read as follows:

GATEWAY=192.168.1.254

Remove or comment it out by prefixing # (hash) :

# GATEWAY=192.168.1.254

Save the file. Add the GATEWAY= to your /etc/sysconfig/network:

# vi /etc/sysconfig/network

Append or modify GATEWAY entry:

GATEWAY=192.168.1.254

Save the file. Reboot the system or run the following command:

# ifup eth0:0

OR

# service network restart

See also:

http://www.cyberciti.biz/tips/freebsd-how-to-setup-2-ip-address-on-one-nic.html

It is possible to create network alias or assign 2 ip address to single NIC under FreeBSD.

My setup:
lnc0 - IP : 192.168.1.1/255.255.255.0
lnc0 alias - IP : 192.168.1.5/255.255.255.255

Note: Netmask must be diffrent otherwise you will get an error ifconfig: ioctl (SIOCAIFADDR): File exists

A) From command line use ifconfig command as follows:
# ifconfig lnc0 192.168.1.5 netmask 255.255.255.255 alias

B) You can setup this alias in /etc/rc.conf file by appending following text, so that next time FreeBSD comes up (after restart/shutdown) it will create alias for you:
ifconfig_lnc0_alias0=”192.168.1.5 netmask 255.255.255.255″

C)Restart FreeBSD network service using following script:
# /etc/netstart

D) Display alias and real ip using ifconfig lnc0 command:
# ifconfig lnc0
lnc0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
inet6 fe80::20c:29ff:fe01:ddbd%lnc0 prefixlen 64 scopeid 0×1
inet 192.168.1.2 netmask 0xffffff00 broadcast 192.168.1.255
inet 192.168.1.5 netmask 0xffff

Read ifconfig man page.