You have multiple workstations with interfaces in both LAN's?
Yes.
Are you guaranteed that the LAN's don't have overlapping address schemes?
Yes.
Ultimately your problem is that you have workstations pretending to also be routers. This violates your edict that the two networks be "self contained", because your workstations are in both networks. It might be easier to put a true router (maybe running Fedora) between this group of workstations and the two nets. That router can run a DNS that dispatches queries to the correct segment, and can centralize the failover logic.
The networks are self contained and the workstations aren't pretending to be routers, they just need access to both networks.
If you need this capability for each workstation, buy cheap Linksys routers, build a custom firmware image with the DNS and failover feature, and flash one router for each workstation. Or script this capability up as something you can run on each workstation to give it the capability.
Carlos
