We have a 3845 router that has a DS3 connection, and a 3825 that has another DS3 connection. I want to stand up a 3845 router with 2 DS3 cards in it. I want to be able to have it as a hot standby router so if one of the other routers go down, the hot standby would take over. Sort of like the failover between two firewalls (a primary and backup). Is this at all possible?
This is exactly what HSRP between two routers does. They exchange hello packets and take over if the other router or the other link is down. With ASA firewalls you probably use VRRP, and HSRP works in a similar way (you could also use VRRP between the two routers).