I need to implement a VPN backup for an MPLS network (running ibgp). I would like to concurrently run a VPN tunnel from a branch office to HQ alongside a MPLS. When the MPLS goes down I'd like traffic to go over the VPN, but only then. I was thinking of setting up the VPN tunnel and doing something like an IP SLA to monitor the MPLS, and maybe add a static for the VPN if it's detected down-- though truthfully, I get it in concept but I'm not sure how I'd implement it. Any ideas? Much appreciated.