EIGRP uses the Diffusing Update Algorithm (DUAL) to provide the best loop-free path and loop-free backup paths.
DUAL uses several terms, which are discussed in more detail throughout this section:
- Feasible Distance (FD)
- Feasible Successor (FS)
- Reported Distance (RD) or Advertised Distance (AD)
- Feasible Condition or Feasibility Condition (FC)
These terms and concepts are at the center of the loop avoidance mechanism of DUAL.