[ILUG-BOM] Backup Internet Line

Raj Mathur raju at linux-delhi.org
Mon May 4 12:34:23 IST 2009

On Monday 04 May 2009, george at annamsoft.com wrote:
> 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.)

What is the equipment terminating the line?

If these are DSL lines, you can set up a Linux box that runs PPPoE for 
all your links directly.  Then it's trivial to be able to determine if 
the link is up or not: if the PPP process of the link is up, you can 
route through it.  Run a small script that checks the link status every 
minute and sets the default route according to which link is up. 
NAT-ing on this Linux box will allow the rest of your LAN to access 
the 'net.

If you're running proper routers for each link, you'll need to write a 
slightly longer script that will check transmission through each router 
and set the default gateway depending on which router is letting 
transmissions through.  Again, NAT your LAN traffic through the Linux 
box that does this.

You can also load balance between multiple links using Linux if you're 
feeling adventurous.


-- Raju
Raj Mathur                raju at kandalaya.org      http://kandalaya.org/
       GPG: 78D4 FC67 367F 40E2 0DD5  0FEF C968 D0EF CC68 D17F
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