This read-write field selects the routing metric for QoS Class 4, typically best-effort, path-selection decisions, completing the set of four independently-tunable per-class routing preferences. An admin most commonly leaves class 4 on administrative-cost, since best-effort traffic usually has the least need for delay or jitter optimization and benefits most from simply using the cheapest available path. For example, setting lportAtmRouteMetricQoS4 to administrative-cost(1) routes best-effort class-4 connections over whichever trunk has the lowest configured lportTrkAdminCost, freeing up the lower-latency paths for the higher QoS classes that actually need them.