[ILUG-BOM] Backup Internet Line

Raghu Prasad prasad.raghu.k at gmail.com
Mon May 4 14:38:56 IST 2009

Hi George!

> I would like to have a backup internet connection to maintain a 100%
> up-time of the Internet.
> We want to achieve this by automatically switching between the internet
> links if it fails (i.e for eg. if the BSNL link goes off, it has to take
> the AIRTEL link and once the BSNL link is ready, it has to switch
> automatically to it.)
> Can anyone throw some guidance on achieving the same.

Checking the link automatically won't work all the time, as mentioned
in earlier posts. But still it may work most of the time. There are
scripts available which can switch the network settings in such a
way that a particular configuration can be chosen from a list of
options. One of the problem in using multiple network interfaces have
been naming the interface reliably. Which card would be eth0 and
which would be eth1? Kernel used to switch cards occasionally
while initializing the network interface. This problem can be solved
now with udev rules.

Once the system names the interfaces correctly, a simple script
can be used to initialize required interface when need arises. In my
setup, I use a script which uses dialog (curses based console UI)
to switch the default gateway. It uses sudo to allow a group of
selected users to do this job. Using a curses based UI allows a
non-technical person to do the required task without getting into
the nitty-gritty of the network setup. This script can be customized
to do automatic switching of the interfaces by adding special
command-line options.

If required, I can provide this script to anyone interested in it.


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