- Maintaining a table of loop-free paths to every destination
- DUAL saves all paths in the topology table.
- Selects lowest cost , loop free paths to each destination
- DUAL enables EIGRP routers to determine whether a path advertised by a neighbor is looped or loop-free, and allows a router running EIGRP to find alternate paths without waiting on updates from other routers.
- EIGRP employs four key technologies, including neighbor discover/recovery, Reliable Transport Protocol (RTP), Diffusing Update ALgorithm (DUAL) finite-state machine, and a modular architecture that enables support for new protocols to be easily added to an existing network.
- DUAL use AD & FD to select the best Path
- An EIGRP router receives advertisements from each neighbor that lists the advertised distance (AD) and feasible distance (FD) to a route.
- AD is the metric from the neighbor to the network. FD is the metric from this router, through the neighbor, to the network.
