Metric and administrative distance for switches

The routing table contains the single best route to each destination that the router has learned. However, a router may learn more than one route to the same destination. The router compares the metrics and administrative distances of these routes to select the best route to add to its routing table.

• Administrative distance: The routing switch uses this parameter to compare routes learned by different routing methods. It indicates how reliable the router considers the method through which it discovered the route. A lower value indicates a more trustworthy route. Administrative distance is not a factor if you are using only static routes. Where the default administrative distances are used, a static route normally supersedes a dynamic route to the same destination because the former has the lowest default administrative distance and metric.

  Routing method	Administrative distance	Metric
  Direct connection	0 (not configurable)	1
  Static route	Default: 1; range: 1–255	1

  To configure administrative distance for a static route, see Configuring static IPv6 routes.

• Metric: The routing switch uses this parameter to compare routes to identical destinations learned by the same routing protocol. The metric is the cost of sending traffic on a given route, and is based on various criteria:

  • Link conditions (bandwidth, delay, reliability)

  • Organizational policies (monetary cost, autonomous systems that a packet must traverse)Each routing protocol has its own method for computing a route's metric. For static routes, the metric defaults to "1" and is not configurable.