EIGRP uses a feasibility condition to ensure that only loop-free routes are ever selected.
These tables are created using information exchanged between the EIGRP routers.
In EIGRP, the information exchanged includes the routes, the "metric" or cost of each route, and the information required to form a neighbor relationship (such as AS number, timers, and K values).
The three tables and their functions in detail are as follows: DUAL evaluates the data received from other routers in the topology table and calculates the primary (successor) and secondary (feasible successor) routes.
If there is no feasible successor in the topology table, a query process is initiated to look for a new route.