DUAL algorithm uses some elements when calculating best routes that packets must travel from one point to another:
- Feasible Distance (FD) - is the best path that a packet must travel to reach it's destination.
- Feasible Succesor (FS) - this is the backup route that packets will use if the primary path fails.
- The succesor is the next router through which packets will be forwarded to.
- There can be multiple paths to a destination point. Routers exchange messages that contain the so called reported distance (RD), this element is actually the FD of a neighboring router. When a route has been chosen we say that the feasibility condition (FC) has been met.
The main element of the DUAL algorithm is the technology used to calculate routes. This mechanism is called a Finite State Machine (FSM). This is actually a logical scheme that is used by the DUAL algorithm to test and choose routes.