This read-write object holds a fourth alternate routing metric for a route entry, with semantics defined by the route's clnpRouteProto value and -1 meaning the metric is unused. An admin would only expect this field to be meaningfully populated for a routing protocol sophisticated enough to report four or more separate metrics per route. For example, a simple statically configured route would leave this field at -1 alongside similarly unused values in clnpRouteMetric2 and clnpRouteMetric3.