Operation of EIGRP

DUAL and the Topology Table

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:

• Successor

• 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.