In the ensari CG page 100:
EIGRP supports unequal-cost load balancing, which allows installation of both successor
routes and feasible successors into the EIGRP RIB. To use unequal-cost load balancing with
EIGRP, change EIGRP’s variance multiplier. The EIGRP variance value is the feasible distance (FD) for a route multiplied by the EIGRP variance multiplier. Any feasible successor’s
FD with a metric below the EIGRP variance value is installed into the RIB. EIGRP installs
multiple routes where the FD for the routes is less than the EIGRP multiplier value up to the
maximum number of ECMP routes, as discussed earlier.
Dividing the feasible successor metric by the successor route metric provides the variance
multiplier. The variance multiplier is a whole number, and any remainders should always
round up.
Using the topology shown in Figure 2-2 and output from the EIGRP topology table in
Figure 2-3, the minimum EIGRP variance multiplier can be calculated so that the direct path
from R1 to R4 can be installed into the RIB. The FD for the successor route is 3328, and
the FD for the feasible successor is 5376. The formula provides a value of about 1.6 and is
always rounded up to the nearest whole number to provide an EIGRP variance multiplier
of 2. Figure 2-14 shows the calculation.
Is there 1 multiplier calculated for each feasible distance? Or is there a base multiplier calculated, for example from the highest (or lowest) FD and then compared? Currently I'm assuming a variance multiplier is caculated for each FD, an FD being a possible backup root if the reported distance on the advertising router is less than the distance calculated locally (to ensure no loops), and the lowest variance multipliers are installed as ECMP routes? Or is there a/one base multiplier that is compared against each possible backup route? Neither the encor or ensari (up the point I've read) have elaborated on this.
