Hello Yuhui,

this is made to influence the choice of best path to primary hub (preferred) in comparison to secondary hub (less preferred)

the lowest bandwidth in path is part of EIGRP metric calculation

256 * (sum of delays in 10s of microseconds)

bw component is the inverse of the smallest BW in the path in kbps multiplied to 256

256 * 10^7/Lowest_BW[Kbps]

Hope to help

Giuseppe