Quote:
Just found out that we have a spare ISDN2 line in the server room, so the ADSL/ISDN option looks good


Just to reiterate: Remember that if you want transparent fail-over for externally-facing services, you'll need to have an ISP that supports that.

If it's just mail, then you can define a secondary MX record for the alternate address, and have it go to the same machine. If it's web, then you need the dynamic routing updates at the ISP.

If, while failed-over, you can live with outbound only, and if your engineers know the alternate IP addresses, so that they can still connect from outside, then you're fine.
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-- roger