This read-write object reports a further alternate routing metric for this route, with protocol-specific meaning and defaulting to -1 when unused. It's one of the additional metric slots, alongside Metric2, 4, and 5, available for routing protocols that expose more than a single metric value for a route. An admin comparing zhIpCidrRouteMetric3 across several candidate routes to the same destination could use it as an additional tie-breaking factor if the routing protocol populates this field.