How do Administrative Distance and metric interact to influence route selection?

• A. The router first selects routes with the lowest AD; if multiple routes share the same AD, it then selects based on the lowest metric.
• B. The router first uses the metric, then AD.
• C. The router always selects the route with the highest AD.
• D. The router ignores both AD and metric when selecting routes.

Answer: (A)

Understanding how a router chooses routes hinges on two values: Administrative Distance and metric. Administrative Distance is a measure of how trustworthy the source of a route is—the lower the distance, the more trustworthy the source. The metric, on the other hand, represents the path cost within that source’s routing protocol, telling how good the actual path is.

The router first compares all candidate routes to the same destination by Administrative Distance and picks the route from the most trusted source (the smallest distance). If there are several routes that come from sources with the same distance, the router then compares their metrics and chooses the route with the lowest cost. This two-step decision-making explains why a route learned from a more trusted protocol is preferred even if another route from a less trusted protocol seems to have a cheaper path inside its own protocol.

For example, a route learned via the most trustworthy source may win even if another route from a less-trusted source has a lower internal cost. If both routes come from the same protocol (same AD), then the one with the lower metric is chosen. If metrics are also tied, other tie-breakers come into play.

So the best answer reflects that process: pick the lowest Administrative Distance first, and if that’s tied, pick the lowest metric.