Thanx for the info, still a few more questions:
1) you said "...what i am trying is that both subnets will be reachable from both sides..." so my question is, reachable on both sides using IPv4 or IPv6 or both?
2) when you did the pings in the last post, what device was doing the pings, and what is it's IPv4 address?
3) also, redo the pings as in last post, but use this syntax "ping fs -4" -4 forces the ping request to IPv4.
In Windows (Vista and newer, and W2K8 and newer), if a network application is executed (ping, RDP, etc) using a name instead of an IP (v4 or v6) address, and the name is resolved in DNS, and the answer is given is IPv4 & IPv6 addresses, Windows uses the IPv6 address first, meaning Windows prefers IPv6 when it gets that info. That is what is you are seeing I believe.
You also stated that you had not configured Vyatta for IPv6, but it is configured for IPv4 - which I assume means it is routing both networks.
Based on the info above, you may want to delete the AAAA Recs in your DNS for all your devices, and then retry pings and RDP's.
You don't actually have a "problem", as much as what is working is not the way you want it to work. Things are working the way they are based on how Windows thinks it should be working - because of Windows default settings and DNS entries. (it's crazy, I know)
hth...Jeff
Jeff Carrell