7.6. IP Aliasing

There are some applications where being able to configure multiple IP addresses to a single network device is useful. Internet Service Providers often use this facility to provide a `customized' to their World Wide Web and ftp offerings for their customers. You can refer to the ``IP-Alias mini-HOWTO'' for more information than you find here.

Kernel Compile Options:

Networking options ---> .... [*] Network aliasing .... <*> IP: aliasing support

After compiling and installing your kernel with IP_Alias support; configuration is very simple. The aliases are added to virtual network devices associated with the actual network device. A simple naming convention applies to these devices being <devname>:<virtual dev num>, e.g. eth0:0, ppp0:10 etc. Note that the the ifname:number device can only be configured after the main interface has been set up.

For example, assume you have an ethernet network that supports two different IP subnetworks simultaneously and you wish your machine to have direct access to both. You could use something like:

root# ifconfig eth0 192.168.1.1 netmask 255.255.255.0 up root# route add -net 192.168.1.0 netmask 255.255.255.0 eth0 root# ifconfig eth0:0 192.168.10.1 netmask 255.255.255.0 up root# route add -net 192.168.10.0 netmask 255.255.255.0 eth0:0

To delete an alias you simply add a `-' to the end of its name and refer to it and is as simple as:

root# ifconfig eth0:0- 0

All routes associated with that alias will also be deleted automatically.