- having a route in the passive state
- having a feasible successor route
- having a route in the active state
- having a successor route
Explanation: EIGRP avoids DUAL recomputation of routes whenever possible by maintaining a list of backup routes (feasible successors) in the topology table already determined to be loop-free. If the primary route (the successor route, which is in the passive state) in the routing table fails, the best backup route is immediately added to the routing table. A route in the active state is in the process of being recomputed by DUAL.