I have 2 site-to-site VPN's one on a 877 and another on a 1841, they both connect to a Cisco 3015 concentrator. We are thinking of getting a second Cisco concentrator with a different internet pipe or use Windows ISA 2006 server for VPN's. Can these routers have a way of using the usual first connect to the Cisco concentrator, but if that is down then go to the new Concentrator or Windows ISA server to establish a VPN?