Diffusing Update Algorithm

DUAL is employed by EIGRP to avoid routing loops. Two metrics are considered by DUAL:

• Advertised distance - The cost advertised by a neighbor to get to a destination
• Feasible distance - The advertised distance + cost get to that neighbor

The feasibility requirement states "if my neighbor's advertised distance is less than my feasible distance, the path will be loop free."

Relevant EIGRP Terminology

• Successor - The neighbor with the best path
• Feasible successor - All other neighbors which meet the feasibility requirement