This the scenario
I have two sites
The sites are connected together by a P2P wireless connection
Windows Servers 2012 on both sites acts as a domain controller. We have one domain for both
DHCP service is enabled in both servers with a failover setting
Users in each site are browsing the internet via two TMG Proxy
The TMG settings are pushed to the users when they login in via GPO setting so the users use the local TMG server as a proxy on their site.
Each site has an individual ISP VPN circuit for getting some applications from a third site. However, currently, both site has a default gateway of the VPN circuit of site 1 so all users are retrieving the applications of the third site via one VPN circuit which is in site 1.
Site 1 ---->TMG1---->Internet
Site 2 ---->TMG2---->Internet
The question is:
How I can force Site2 to go through VPN2 to retrieve
Site 3 applications when the Wireless link is dropped? In different words how I can configure site 2 to use VPN 2 as a gateway in only that case (Wireless connective is dropped) without changing the current configuration of the DHCP.
Both VPNs can see each other as they are already configured to do so by the ISP.