I have a client with a set-up like this (All routers are Cisco 2600 using IOS 12.2 or later):
Internet | | Router A | | NVPN Cloud / \\ / \\ / \\ Router B Router C | | Internet
Each router is at a separate physical location. Router A is at the main branch and has a T3 to the internet. Router C is at a branch office and has a fractional T1 to the internet which they intend to use as a backup in the event the T3 goes down. Router C should always utilize the path through Router A unless it is down as they have web monitoring configured in the main branch which all branches must use unless they fail over to the backup. They are currently using RIP V2 to advertise their routes through a NVPN to eachother. According to their internal IT people, they are only able to utilize RIP and not OSPF or EIGRP due to some constraints of their ISP. I am currently checking to see if this is in fact correct or if they can actually use a better routing protocol (as I suspect) and have been misinformed.
I had a thought to configure a static default route on each router through Router C with an AD of 254. If anyone has a similar configuration and can provide a sanity check on my idea or perhaps a better idea, it would be greatly appreciated. Please respond understanding that I fully intend to implement a better routing protocol if at all possible and am simply looking for a possible solution in the event that I CAN'T change it. Thanks in advance for your input.