Using a Linux failover router
In this article we will look at setting up an existing Linux machine as a failover router to provide quick and automatic switchover from a dead Internet connection (the primary connection) to one that is operational (the secondary connection).
To begin, you'll need a PC with any recent GNU/Linux distro installed. You'll also need three network cards to put into this Linux box. Two of the three network cards, say eth0 and eth1, will connect to the Internet routers/gateways of your primary ISP (say ISP1) and secondary ISP (say ISP2). The third network card, say eth2, will connect to your internal LAN.
By Rohit Girhotra at Linux.com
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