Setting a Variance of at Least Twice the Metric

D

The correct answer is D. unequal cost load balancing.

Unequal cost load balancing is a feature of routing protocols that allows for the distribution of traffic across multiple paths with different costs, also known as metrics. By default, routing protocols choose the path with the lowest cost to reach a destination. However, with unequal cost load balancing, the router can use multiple paths with different costs to reach a destination and distribute traffic across those paths.

To configure unequal cost load balancing, the router needs to be configured with a variance that is at least two times the metric. The variance is a multiplier used to increase the metric of feasible successor routes, which are alternative paths to the destination that have a metric that is less than the current best path.

For example, let's say that a router has two paths to reach a destination network: Path A with a cost of 10 and Path B with a cost of 20. By default, the router would choose Path A as the best path. However, with unequal cost load balancing and a variance of 2, the router would also consider Path B as a feasible successor with a metric of 40 (20 x 2). The router would then distribute traffic across both paths.

Therefore, by setting a variance that is at least two times the metric, the router can enable unequal cost load balancing and distribute traffic across multiple paths with different costs.