Hi guys,a customer of ours used to work with a DOS-based application and product catalogs on CD-ROM. Now they moved to an internet-based solution of the product supplier. As a matter of fact, they now heavily rely on a working internet connection...
They now have a DSL flatline but sometimes - you know - DSL is down for a lot of prossible reasons... anyway: The customer still has ISDN available - that's why I am in search for a solution that allows the LAN machines to get their internet connection via ISDN if the DSL line is down.
They have a DSL broadband router with integrated DSL modem (Zyxel model, dhcp enabled) which supports up to 4 machines plugged in directly. Currently, 3 machines are connected. So much for the DSL.
We can set up an additional machine for the ISDN connection with automatic dial on request... but how to configure the actual "fallback" logic?
Can this be done by simply specifying 2 gateways in the appropriate order (eventually turning off the dhcp stuff if required) or do we need some kind of script(s) that control the connection state and eventually set/change the default route? (I found some approaches like that being discussed in unix/linux forums - but hey... really?)
I would prefer to keep it as low-level as possible, that's to say "tcp/ip-based only" solution first, then software-controlled solution, then (last option): Get a different DSL/router with modem and integrated ISDN fallback.
But there MUST be a way of doing it without the need for a hardware-based fallback, right? 
Although not the preferred solution, I would also appreciate if someone tells me how to set up IDSNPM to run both connection types and handle the fallback internally.
Thanks for any suggestions / hints / tips...
Greetings
Thomas