I have two laptops that I use and control them using a single keyboard. One has a cisco vpn client that I use to connect to work and usually both machines are connected via airport. When I connect to work using the vpn, I can plug in an ethernet cable but can't connect to the other machine. The target machine shows up, but I get an error connecting to it.
My home lan has a NAT device so that all my IP's are in the 192.168.1.x (both for airport and ethernet).
I can sometimes delete the trusted host on the target and turn everything off, and then start it back up and sometimes get it to connect. I have better success doing this if I re-arrange the ethernet and airport ports in network prefpane.
I think it would be good to be able to specifiy the port the connection is using, and more importantly to be able to manually enter trusted machines on the - then I would be able to enter the other IP address that is in use.
This problem would also be solved if bonjour was supported as bonjour seems to always work, even if I'm on the VPN using a single interface. (e.g. the non vpn "target" machine can see the other machine via bonjour but not by it's assigned IP address).