lan with failover internet connection (adsl)

"For this sort of thing, If you want a pure off the shelf hardware solution that does not involve custom software or tinkering, I would recommend a Draytek router.

They work very well, typically it is a modem/router itself and has one standard ethernet port for failover, so you would connect an existing router into that and you can configure it for failover or bonding.

Drayteks are great, you can even plug in a 3g usb card to use when the connection fails!

Remember though, if you are doing this purely for resilience, having two ADSL connections may not ""save"" you. I am guessing that most countries would be similar to the UK, the connections will terminate at the same exchange so whilst having two connections will help against an ISP doing maintenance (If you pick two different ones), it will not prevent you from other ""unplanned"" problems that is responsible most of the time for disconnections."