adjacent router
neighbor router


Two seperate route in eigrp topologi tabel:
1. Successor route (SR) = primary route
2. Feasible successor route (FSR) = backup route
3. Feasible condition (FC)  --> AD FSR < FD

Actor:
1. Upstream neighboring router
2. Particular router

From R1 perspective, R3 is advertising a distance
of 10000 to the detination 10.22.55.0/24
however your distance to R3 from R1 is 500,
so your feasible distance would be 10500