Systems and techniques, including special messages and state machines, are described that configures an intermediate site to dynamically trigger creation of and removal of a dynamic conduit between two sites based on usage that is tracked at the sites. The intermediate site providing WAN-to-WAN forwarding between the two sites, monitors throughput statistics on each local WAN link (LWL) associated with the two sites. If traffic between the two sites passes a configured first threshold or if LWL usage passes a configured second threshold, the intermediate site sends a message to the two sites to set up a dynamic conduit directly coupling the two sites. Busy lists are used to keep track of eligible site pairs. Once a dynamic conduit is set up between two sites, a grow technique tests the dynamic conduit increasing communication flows between the two sites each configured sampling period before putting the conduit in normal use.