EIGRP Terminology

(c) CBT nuggets

AD - advertised distance. For example 1900 in our case for net 10.1.2.0./24
FD - Feaseble distance = AD + cost. For example FD (R1) = 600 +10 for net 10.1.2.0./24
Successor - Primary route ( goes to the routing table)
Feaseble Successor - backup route. Must match condition - AD must be less then FD of the successor
Active route - route is actively search (DUAL) for path to net. Smth failed. If there is feaseble successor, backup route goes routing table without recalculation
Passive route - everything allright.

Feaseble successor shows in topology table #sh ip eigrp topology