We're managing a network consisting of 1 HQ and 4 remote sites. The remote sites are connected via a leased line of 2 Mbps. The remote sites have got 1 small Cisco router provided by the telco provider which provides the connectivity to the HQ. The HQ itself has got 2 (or maybe 3) Cisco routers which provide the connectivity to the remote sites.
What we want is an economic failover for the connectivity in case a leased line goes down (which happens too often, although we've got a SLA with the provider). Anyway, we were thinking of purchasing a separate Internet Line in each site (incl HQ) and a small appliance doing VPN (Astaro, Juniper or that kind of stuff).
The problem would be to tell the network/client that the leased line is down and to route the traffic through the VPN line.
What's the best way to do that?