Most redundant links today are made up of active or passive paths. There are two ways in and out of the network, but only one way will actually be available at any given time. The path passing traffic is called the active path, and the one standing by in the event of a failure is called the passive path.
HSRP, VRRP, spanning tree protocol (STP), and Dynamic Routing Protocols, such as, OSPF, EIGRP, and BGP, are arguably the most common technologies used to automate network failover. Admittedly, many of these include options to balance traffic, but they are historically configured to allow for one path to pass traffic at a time.