|Not enough info. What are the four links of the routers? What type of routers? What type of switch?|
It sounds like your would be talking about HSRP (Cisco term for hot-standby-router-protocol) where if one router fails then the other router keeps internet traffic going...i.e. read this link:
Other manufactures have similar capabilities but call it something different.
Since have no ideal what routers you are using can not help you determine the equivelant configuration, if any in your product.